Scroll thru this sub for some recommendations, but DO NOT get a D3.0 modem! ISPs are phasing them out, and Xfinity probably won’t even let you add it to your account.

Check out the Arris SB8200 or the S33.

And check with your ISP (they have a supported modem list on their website) before you buy anything…

Nobody actually uses Cat8, not even datacenters (we just use fiber or DAC). The wiki article says it was designed for it, but it’s less reliable, has more overhead, and is more power hungry, so it never caught on.