Optimizing Speed with Netgear Nighthawk CM1200 Modem

Recently switched from Xfinity provided XB6/ARRIS TG3482G to a Netgear Nighthawk CM1200 Modem. The Xfinity provided router/modem combo was plugged into my UniFi USG, which is also a router, which basically meant I had 2 routers unecessarily, plus I was paying monthly to rent the Xfinity device. So I plugged the Nighthawk (3.1 DOCSIS modem only) into the UniFi USG, expecting better results than before (approx 200mbps down for "up to 500mbps" advertised speeds). To my surprise, I experienced worse speeds after the switch. I called Netgear and they told me the downstream and upstream power values were not set optimally for the modem and to contact Xfinity to have them change it. Netgear recommended ranges of -7 -> +7 for downstream power and +38 -> +48 for upstream. I'm currently showing ranges of -10.3 -> -12.3 for downstream and 50.5 -> 52.5 for upstream. I called Xfinity and they told me they can't make those changes, and that they'd need the modem to be active for 7 days before they can see a "historical plot" of its activity. Any advice for where to go from here?