I recently upgraded to 1 Gbps service on Comcast but cannot get over 300 Mbps on my Samsung Galaxy S9+ or my laptop using a Killer Wireless 1435 NIC. I sometimes test under 200 Mbps at speedtest.xfinity.com. It doesn't seem to matter if I connect (5 Ghz specifically) to my Nighthawk R7000 or the modem / router gateway they provided. I split the signal on both to be sure I was connecting 5 GHZ. The S9+ and Killer Wireless 1435 are both rated for over 1 Gbps.
It's the one Comcast provides for their 1 Gbps service.
It doesn't appear to have a name on it. I've been meaning to connect directly Cat 5E or Cat 6 but haven't yet. I had bought and connected a Netgear CM1150V but was not getting over 300-400 Mbps when I connected wired directly. They came out, said their equipment couldn't connect to any other equipment than their own to test, and I gave up and let them put in their rental modem. I foolishly trusted the tech when he tested it at around 900 Mbps.
I'll test wired directly to their gateway tonight.
I tested wired direct to the Comcast modem and got 872 Mbps down and 42 Mbps up. Then wired to the R7000 and got 715 down and 42 up. I also tightened the antennas and got 320 down and 42 (41.7) up on 5G WiFi. I think it was around 400 down connect to the Comcast 5G but still around 42 (41.7) up.
SGS9+ did 322 down and 41.3 up connected to Netgear Nighthawk R7000 router.