Here is a break down.
SB6120:4 channels down, 4 channels up(4x4). Still the gold standard.
SB6121:4x4, new case, MoCA filter.
Update:
Found this on a off site review of the SB-6121. This might work for users of this model on Time Warner Cable ISP Services- Not guaranteed though."
I didn't feel like paying TWC money to lease a modem. I talked with multiple reps at Time Warner Cable (TWC) and they all said that they do not support the SB6121, but do support the SB6141. I really didn't want to spend $125 on a modem and because of someones post about how they have to support it (FCC regulations), I decided to buy one of the used SB6121 modems for $65. Once I was able to speak with someone at TWC (took 30 minutes of holding) I told the rep my MAC address, but told them my model number was SB6141 (supported in my area). Because the MAC address is the only thing that matters and they just wanted to check that I had a supported device there was no arguing and it took all of 2 minutes to activate. Again this was after two different reps told me the SB6121 would not work on their system.
I have only been using the modem for a short period of time, but have not had any problems. My ping time increased by about 5ms (not sure why), my upload speed didn't change, but my download speed increased by 5 to 10mb/s. This was without changing my internet plan."
SB6180:8x4, new case, MoCa filter. Very hard to find.
SB6580:8x4, new case, MoCA filter. Modem/Router Combo
SB6141:8x4, new case, MoCA filter. Short answer, its uses a different tuner then the SB6180. Similar performance.
SB6183: Arris Branded
16x8,
SB6190: Arris Branded
32x8,
https://www.dslreports.com/forum/r31079834-ALL-SB6190-is-a-terrible-modem-Intel-Puma-6-MaxLinear-mistake