Best SLI option for nVSurround

[Avalanche]

So I have a new setup arriving next week and I'm going to need to add some horsepower to run it. I want to run BF3 multiplayer at 5760x1080 (or I guess 6010x1080 to compensate for the bezels) and have been looking at snagging some cards to do so. I'm currently looking at the 670 or 680, and will be buying two of whichever I go with. From what I've seen is that at that resolution it may be bottlenecked by the 2GB VRAM.

I've been looking at buying two of the EVGA GTX 670 FTW+ 4GB cards, but I've seen others that say that the 670 doesn't really get a performance increase from the added VRAM.

Also, will the fact that my motherboard is only PCIe 2.0 be an issue?

Displays are 120Hz 24" BenQs.

I guess the main question is can I get away with 2GB cards at that resolution and go with 680s, or go 4GB and go with 670s? Trying to stay around $1000.

 

[Astrodave]

I run BF3 with settings on ultra/high at 5760 on dual 480's and I see 40-70fps with smooth play averaging in the 50's usually. The only time you'll need that vram is with higher levels of AA but nvsurround disables all AA higher than 2 by default anyway. So far I have had absolutely no reason to upgrade my system from my 480's as every game I play still runs great in surround and most even in 3DVS as well.