WEP is encryption, it's just very weak. WEP128, WEP64 and unencrypted should all be the same speed since these are done in hardware.
Orinocos can perform WPA/TKIP encryption, but the firmware doesn't work with many modern routers. True Prism-II cards are more compatible and also support WPA2/AES/CCMP, but would be extremely slow with WPA/WPA2 on a stock A1200.
