Originally Posted by phantasmor
really? choke on vram? if sli only uses one card's vram, maybe, i don't know for sure
but if both card's ram is used i don't see vram really being a factor
The vram in SLI and Crossfire work kinda like a RAID-1 array of disks in terms of their 'storage capacity'
IOW, the effective vram capacity of all the cards in a multi-gpu setup is = whatever card has the lowest memory capacity in the set.
Just like with multiple HD's in RAID-0, in SLI/Xfire, the same data has to be mirrored across all the cards in the set.
@OP: personally, I'd stick with the SLI 570's you've already bought ... unless you need the $200, or you find some crazy good deal on a 580.