The biggest cause for slow browsing is having Power Saving mode enabled on the X50 wifi interface.
The guide that ironhelix is referring to is here:
http://wifi.aximsite.com
I've done some testing with encryption and unless you are doing the encryption with some additional third party software you'll see no decrease in speed. Over a 80MB file I saw something like a 2 second increase when comparing WEP with no WEP. If there is software AES being done then there will be a much larger increase in time to download. But for WEP and WPA you should see no significant increase in time to transfer.