from my own testing, platorm is a
[email protected] with 8gb RAM, 1920x1080
GTX560ti 1GB - High Preset - fine and smooth - Ultra preset - turns in to slide show
GTX560ti 1GB SLI - High preset fine and smooth - ultra preset = slide show
Any combination of settings that keeps the VRAM usage below 1GB (e.g. 900mb ish) is fine but ultra textures or msaa push it over that and fps falls off a cliff
GTX 580 1.5gb High preset - 70-80FPS Ultra preset 40FPS with stutters, on large maps like caspian border 64 I can see objects appearing out of nowhere (VRAM usage over 1.5gb), not internet/ping related as dropping msaa lower VRAM usage and everything is then smooth with no issues (objects appearing out of nowhere also doesn't cause FPS drop but it is noticeable and annoying).
GTX 580 3GB - ultra preset - 50fps avg. with occaisional drops to 40, no problems with textures loading on the fly, no stutter (VRAM usage 1800-1900mb)
new system build put on hold until a 2nd GTX580 3GB can be nabbed