Router Speed Slower than Modem Speed

I currently have the 200MB download and 14MB upload internet plan from Xfinity. I own my own equipment and recently upgraded my wireless router to the Netgear Nighthawk 7200. I immediately saw an increase in speed, as my old router was a 802.11g. However, I still wasn't getting anywhere near 200MB (in fact, less than 100). I decided to upgraded my cable modem to the Arris SB8200 Gigabit modem. When I connect via ethernet to the modem and conduct a speedtest, I get 200MB down. However, when I connect wirelessly through the modem the speed is reduced to about 90MB. I've researched numerous forums trying to figure out if there are settings on my router that are dampening the speed. Nothing so far has worked. Hoping someone can help!