I'm guessing it's because I'm still 32Bit? I also only have 4GB of RAM..
I just find it weird that I'm able to launch "Instant Action" without a hitch, and when it launches it flys beautifully, no stutters, nice and smooth...
Core 2 Quad Q6600 @ 2.40GHz, 4GB RAM, Radeon 6900 HD 2GB, 32-Bit Win Vista
edit: I did not delete the saved game folder.. I'm guessing you are referring to User/Saved Games/DCS?