iPhone wifi speeds are less than 3G on my new network after setting up AE

Hello everyone. I've been searching long and hard for an answer with no success. I'm hoping someone here can help me out. A few weeks ago I upgraded my speed on my ISP from 30Mbps down and 4Mbps Up to 50Mbps down and 8Mbps up. I used to have a WRT54G Linskys router which gave me great speeds on my ipads, iphone, Apple TV and both windows based computers. The other day I switched the Linskys out for an new AirPort Extreme. I Set it up and the speeds on all my devices were constant around 35 down and 8 up. I left the default settings on the AirPort Extreme. Then a few days ago I set up the security for my router, WPA2- Personal. Checked the speeds and my computers, ipads are running great but now my iphones are doing constantly for the last 3 days 1Mbps down and 8Mpbs up. So last night I tuned off my security and than the iphone was back to normal speeds. I'm pretty much confused now. Any ideas? Seems like the security setting are doing something here