Fast LAN speed/slow WiFi speeds

Hi,

 

I've got the WNDR4300 with the latest firmware.

I use an Arris cable modem (I have that set to bridged so it won't double up on the NAT).

My Internet speed is 200mbps and I get that on my desktop PC which is wired into the router.

On WiFi, though, even when I'm right in front of the router, I can't get any speeds faster than a max of 35mbps which seems really low. I've tested with an iphone 5, a laptop and a Kindle Fire HD and they all get about that speed (using the Ookla speed test).

 

Thanks :)