Since the engine streams everything via the HDD, a SSD will indeed make a world of difference.
Previous - C2D 9800, 8G RAM, and a GTX 260.
Current - i7-980 Extreme, 6G RAM, and a GTX 480.
I saw little to no improvement whatsoever after switching systems, even ran benchmarks to see if there were any drastic performance differences. There weren't. Minimal at least. After installing ArmA II and OA on my SSD, my FPS shot up to a stable 40-60, and that is with almost all options set to very high, with a 200% texture resolution.