I'm having the same issue with my 6235 (when it works at all). My connection is 50 down / 30 up, but on wifi I only get 15 down, 20 up.
Please try to enter the following command in cmd: netsh wlan show interface
This is for you to check the transmit and receive rates. Let me know if you get 150 Mbps which is your router's fastest speed or if you get something else.
I switched N back on (keep it off because it drops my connection) and I got 300! So I guess my router is the bottleneck?
Of course within 20 seconds of doing that I lost wifi, so I had to disable N again. Back to 54 mbps!
a helpful man on superuser.com helped me out on this thta maned to solve it! Seems like bluetooth cannot be running if we want the full bandwith