Are these performance issues a RAM thing?

I'm getting pretty subpar performance with my system (listed below). It manifests itself most noticeably in WoW, a game which obviously no current machine should be having trouble with. The issue is threefold. First, very significant stuttering and pausing, upwards of half a second, when rapidly changing the field of view. Second, near-constant, quite small but very annoying mini-stutter (not "micro," this isn't a dual-core GPU) when moving; it's most easily detectable at the sides of the screen, and basically it looks like the game just drops some frames every few seconds. The actual framerates are generally okay, and they don't seem to decrease when this happens. Third, pretty ridiculous texture popping, especially with shadows, which happens in all games--Far Cry 2 and Crysis Warhead look particularly awful.

So I ran Memtest overnight and it picked up an error after several hours. Is this the kind of thing that can be explained by bad RAM? Or does it sound like something else?

Specs:
C2D E8500
Raderon HD 4870
Asus P5Q Pro mobo
4GB OCZ Reaper DDR2-800
WD 640GB HDD
Vista 64