Paying for 1100 mbps and getting around 300 mbps

I did a quick assessment with the xfinity chat bot and it mentioned my equipment not being compatible. I'm using an Aris Surfboard SB8200 modem connected to a Netgear Nighthawk X6 R8000. These should capable of running 1100 mbps speeds. When I run the xfinity speed test, I connect directly using an ethernet cable and through wifi and they are about the same (300 mbps). How do I get what I'm paying for?