I recommended [H] because they've done an excellent analysis of the IQ of the different AA modes so you can decide for yourself if you "need" 4xMSAA. Running on default ULTRA enables 4xMSAA AND post AA, but once you have post AA enabled it is pointless to have MSAA on.
I already said NV cards performs better with MSAA. With it off, AMD cards usually have the edge.
BF3 is a unique game in that settings on ULTRA will use extra VRAM if you have it. Its used to stream in higher res models/textures at a further view distance so the game looks better the more vram you have. This only occurs on ULTRA settings. On High, the game should not be streaming above 1gb vram. It's an automatic feature.
So unless DICE is lying in their presentations, on ULTRA, a 2gb vram gpu has higher res models/textures further away than a 1gb or 1.25gb vram gpu.
ps. ~40 fps in SP is unplayable in MP.