According to poll, comments on Bi forums that massive FPS drop from 60 to 1-2 when the game becomes completely screwed is in 90% happening on 32bit OS. And it really doesn't matter what your rig is. (must be able to handle at least the Stratis ofc.)

check this thread and vote! http://forums.bistudio.com/showthread.php?162402-1-2-FPS-on-Altis-and-60-fps-on-stratis [^]