If you pay for gigabit cable internet and still run your ISP’s rental modem, you’re paying $15–20/month for hardware that will break even against a decent replacement in under a year. The math is simple: at $15/month, a $150 modem pays for itself in 10 months. But picking the wrong modem wastes that savings — cable ISPs maintain strict compatibility lists, DOCSIS 3.1 is the floor for actual gigabit throughput (not marketing gigabit), and a modem that isn’t on Comcast’s or Cox’s approved list simply won’t activate regardless of its spec sheet.
DOCSIS 3.1 supports downstream speeds up to 10 Gbps across two OFDM channels (each up to 192 MHz wide), compared to DOCSIS 3.0’s theoretical maximum of roughly 1.2 Gbps across 32 bonded channels. In practice, most cable plants today deliver somewhere between 900 Mbps and 1.2 Gbps to end users on gigabit tiers, which means a DOCSIS 3.1 modem is necessary but not sufficient — you also need to verify that your specific ISP has provisioned the modem model you’re buying. Comcast Xfinity, Cox, Spectrum, and Mediacom all publish compatibility lists; cross-reference before purchasing.
One more thing the marketing materials won’t tell you: multi-gig plans (2 Gbps+) require DOCSIS 3.1 modems with a 2.5GbE or faster LAN port, not just a standard gigabit Ethernet port. A modem with a 1GbE WAN-facing port is a hard cap at ~940 Mbps regardless of what the cable plant can deliver. That distinction matters if your ISP offers 1.2 Gbps tiers — and it matters even more if you’re planning ahead.
Quick Comparison
| Model | DOCSIS | Downstream Channels | Max Speed | LAN Port | Compatibility | Price |
|---|---|---|---|---|---|---|
| ARRIS SURFboard SB8200 | 3.1 | 2x OFDM + 32x SC-QAM | 10 Gbps (spec) | 2× 1GbE | Xfinity, Cox, Mediacom | ~$130 |
| Motorola MB8611 | 3.1 | 2x OFDM + 32x SC-QAM | 10 Gbps (spec) | 1× 2.5GbE | Xfinity, Cox, Spectrum | ~$150 |
| NETGEAR CM1000v2 | 3.1 | 2x OFDM + 32x SC-QAM | 10 Gbps (spec) | 1× 1GbE | Xfinity, Cox, Cox | ~$120 |
| ARRIS SURFboard SB6190 | 3.0 | 32×8 SC-QAM | ~1.4 Gbps (spec) | 1× 1GbE | Wide | ~$70 |
| Motorola MB7621 | 3.0 | 24×8 SC-QAM | ~960 Mbps (spec) | 1× 1GbE | Xfinity, Cox, Spectrum | ~$80 |
Prices are approximate at time of writing. Verify ISP compatibility at your provider’s modem approval page before purchasing.
ARRIS SURFboard SB8200
The SB8200 has been the default recommendation for Xfinity gigabit subscribers for several years, and with good reason: it ships with two 1GbE LAN ports (link-aggregatable to ~2 Gbps with a compatible router), supports DOCSIS 3.1 with 2 OFDM downstream channels and 2 OFDMA upstream channels, and ARRIS maintains an unusually clean firmware update track record compared to budget alternatives. It’s on Comcast’s approved list, Cox’s approved list, and Mediacom’s — three of the four largest US cable ISPs.
The dual 1GbE ports deserve a closer look. Most users connect only one to their router, treating it as a standard single-port modem. But if your router supports link aggregation on its WAN port (the ASUS RT-AX88U and several Netgear Nighthawk models do), you can bond both ports for a practical ceiling of ~1.8 Gbps — relevant if you’re on a 1.2 Gbps tier. The chip inside is a Broadcom BCM3390, the same silicon that powers most of the DOCSIS 3.1 field, which means driver maturity and ISP firmware support are solid.
One known limitation: the SB8200 is not on Spectrum’s approved modem list. Spectrum (Charter) operates its own equipment policy and in most markets requires you to use their rental modem, though they’ve expanded third-party compatibility in some areas. If you’re a Spectrum customer, verify your local market before buying. For Xfinity and Cox gigabit subscribers, the SB8200 at ~$130 remains the value anchor of this category.
Motorola MB8611
The MB8611 is the spec-forward answer to the SB8200’s dual-port compromise. Instead of two 1GbE ports, it ships with a single 2.5GbE LAN port — a more elegant solution for the 1.2 Gbps subscriber who doesn’t want to deal with link aggregation setup. Connect it to any router with a 2.5GbE WAN port (the TP-Link Deco XE75, ASUS ZenWiFi Pro ET12, and Netgear Orbi RBK863S all qualify) and you have a clean path to multi-gig throughput without bonding configuration.
Under the hood it’s also DOCSIS 3.1 with 2 OFDM + 2 OFDMA channels and 32 bonded SC-QAM downstream fallback channels for compatibility with older plant infrastructure. Motorola lists it as compatible with Xfinity, Cox, and Spectrum — notably including Spectrum, which the SB8200 does not. The firmware update history is reasonable; Motorola has been more consistent than some third-party modem vendors about pushing security patches, though ARRIS’s enterprise background gives it a slight edge in long-term support longevity.
At ~$150, it’s the most expensive DOCSIS 3.1 modem on this list. That premium buys you the 2.5GbE port and Spectrum compatibility — if neither matters to you, the SB8200 is $20 cheaper for equivalent downstream performance. If you’re on a 1.2 Gbps plan or expect to upgrade to one, the Motorola MB8611 earns its price difference.
NETGEAR CM1000v2
The CM1000v2 is NETGEAR’s current DOCSIS 3.1 modem, the revised version of the original CM1000 with an updated Broadcom BCM3390 chipset. It supports 2 OFDM downstream channels, 2 OFDMA upstream channels, and 32×8 SC-QAM fallback bonding. The LAN port is a single 1GbE — no link aggregation option, no 2.5GbE — which caps practical throughput at ~940 Mbps even on a gigabit plan. That’s fine for most users on a true 1 Gbps plan; it’s a consideration if your ISP sells 1.2 Gbps.
NETGEAR’s compatibility story is more conservative than Motorola’s or ARRIS’s. The CM1000v2 is certified for Xfinity and Cox; Spectrum and Mediacom support varies by market. NETGEAR also maintains a useful compatibility tool on their site that takes your zip code and ISP and confirms whether a specific model will activate — worth using before purchase rather than after.
Where the CM1000v2 competes is on price and NETGEAR’s brand recognition with ISP provisioning teams. In practice, NETGEAR modems tend to activate cleanly with ISP support staff who are less familiar with Motorola’s product line. At ~$120 it’s the cheapest DOCSIS 3.1 option here, and the build quality is solid. If you’re on Xfinity or Cox and want a set-it-and-forget-it modem without paying for features you won’t use, the NETGEAR CM1000v2 delivers.
Motorola MB7621
The MB7621 is the right answer for a specific situation: you’re on a cable plan that tops out at 800–960 Mbps and your ISP doesn’t yet support DOCSIS 3.1 provisioning in your area (this is more common in smaller markets and rural Spectrum footprints than the marketing suggests). It’s DOCSIS 3.0 with 24×8 SC-QAM channel bonding, a theoretical downstream of ~960 Mbps, and a single 1GbE LAN port. No OFDM, no DOCSIS 3.1 overhead, no firmware complexity associated with multi-standard support.
For ISPs that haven’t fully deployed DOCSIS 3.1 plant upgrades, a well-provisioned DOCSIS 3.0 modem can sometimes outperform a DOCSIS 3.1 modem that’s falling back to SC-QAM channels anyway. The MB7621’s channel bonding handles congestion and noise margin degradation well, and Motorola’s provisioning compatibility is broad across Xfinity, Cox, and Spectrum. It’s also the cheapest reliable option here at ~$80.
The honest caveat: if your ISP already runs DOCSIS 3.1 in your area and you’re paying for a gigabit tier, the MB7621 is a ceiling. It cannot negotiate DOCSIS 3.1 — you’re locked to its SC-QAM channel set regardless of what the headend supports. Buy it if the price delta matters and your plan tops out at 800 Mbps or less; skip it if you’re on a true gigabit or higher plan.
ARRIS SURFboard SB6190
The SB6190 is DOCSIS 3.0 with 32×8 SC-QAM bonding — the maximum channel count for the standard — and a theoretical downstream of ~1.4 Gbps. At ~$70 it’s the cheapest modem on this list, and it has a long-established presence on ISP compatibility lists across Comcast, Cox, Spectrum, and others. The hardware has been in the market long enough that firmware is stable and provisioning is well-understood.
Why it still makes the list despite DOCSIS 3.0: for users on plans between 400–800 Mbps who want to stop paying rental fees without paying a DOCSIS 3.1 premium, the SB6190 is financially rational. The $60 price gap between it and the CM1000v2 covers three months of rental fees. If you’re not planning to upgrade your internet plan within the next two years and your current speed is under 800 Mbps, DOCSIS 3.1 is paying for future-proofing you may not need.
The known issue with the SB6190 is an older Intel Puma 6 chipset variant in early production runs — a documented high-latency bug under certain traffic conditions. Later production runs and the current stock use a revised silicon path that doesn’t exhibit the problem, but it’s worth verifying the hardware revision if you’re purchasing used or from third-party sellers. Buy new from a reputable retailer and you’re unlikely to encounter it.
Who Should Buy the SB8200 vs. MB8611
Buy the SB8200 if: you’re on Xfinity or Cox on a 1 Gbps plan, you have or plan to get a router with link aggregation on its WAN port, and you want the best combination of price and firmware pedigree in DOCSIS 3.1. The dual 1GbE ports give you a path to ~1.8 Gbps throughput without replacing the modem, which is relevant as Xfinity expands its 1.2 Gbps tier. It’s $20 cheaper than the MB8611 and has the longer track record.
Buy the MB8611 if: you’re on Spectrum (where the SB8200 isn’t supported), you’re already on a 1.2 Gbps plan and want a single clean 2.5GbE handoff to your router without configuring link aggregation, or your router has a 2.5GbE WAN port and you want to use it. The 2.5GbE port is genuinely useful today if your hardware supports it — it’s not a spec for a future that hasn’t arrived yet.
Buy the CM1000v2 if: you want DOCSIS 3.1 at the lowest current price point (~$120), you’re on Xfinity or Cox, and you don’t need multi-gig throughput now or in the near future. It’s the pragmatic choice.
Buy the MB7621 or SB6190 if: your plan is under 800 Mbps, your ISP may not have fully deployed DOCSIS 3.1 in your area, and your priority is eliminating the rental fee at minimum cost. Both will do the job cleanly at a price that breaks even against a $15/month rental in under six months.
Bottom Line
For most gigabit subscribers on Xfinity or Cox, the ARRIS SURFboard SB8200 is the right buy: DOCSIS 3.1, proven ISP compatibility, dual 1GbE ports, and ~$130 price point that breaks even against rental fees in under nine months. Spectrum subscribers should go straight to the Motorola MB8611 for its Spectrum support and 2.5GbE port. If you’re on a sub-gigabit plan and just want to stop paying the rental fee, the Motorola MB7621 at ~$80 gets the job done without overbuying.