Wifi vs ethernet - XFinity

With my current router I lose1/2 my speed at the furthest point in my house from router. To be honest I don't think it is that far (maybe 20 ft. and through a basement floor only). I plan to do one of three things...extender, access point or new router. Can I hope to get speeds comparitive to my ethernet connections? I lease a gateway from Comcast. Should I just go new modem and router and see what that gets me? I currently have a 75mbps connection which constantly shows around the 90s on my current ethernet connection. I don't need this much but am afraid if I go for a slower plan my wifi speeds may drop too far. I'm in a quandry...