I get 120 Mbps down on a 75 Mbps Xfinity plan. I think. My bill says I have “Performance Pro Internet”, which appears to be specced for 75 Mbps download. I'm

I get 120 Mbps down on a 75 Mbps Xfinity plan. I think. My bill says I have “Performance Pro Internet”, which appears to be specced for 75 Mbps download. I'm using an Arris (née Motorola) SB6183 modem. fast.com and speedtest.net both report that I'm getting 120 Mbps down. (I'm pretty sure that I signed up for 75 Mbps down, but Xfinity makes it really hard to figure out what service you're using.)