I noticed since Armed Assault Streams the island from your hard drive, I have seen quicker load times and overall better game play from a friend of mine computers who's only difference is his hard drive being a SATA 3.0. The higher 3.0 Gbit/s seems to make a world of difference.
The rig he has is the following:
P4 2.8 Single Core
9600XT AGP Video Card
SATA 3.0 Hard Drive
His Armed Assault Perfromance is Amazing as far as Ingame.