They have 1.28GB each. As MecBlade has already said, you are running into a massive vRAM bottleneck. A GTX 570 (1.28GB also) and a 6970 (2GB) are pretty much neck and neck up until 1080p. At 2560 x 1440 the 6970 pulls ahead significantly, because vRAM becomes a limiting factor for the 570. I can only imagine what levels of vRAM you'll require for 3299x1920. I'd say 2GB 6970s, 2.5GB 570s or 3GB 580's would be your only real options. Remember that though the cards might have 1.28GB each, this does not equal 3 x 1.28GB (3.84GB) - as SLI only uses the vRAM on a single card. You have a heck of a lot of GPU core power being underutilised there.
Yes I am As Parge has said, SLI does not scale and utilise the memory on all the graphics cards. It will only take advantage of the one which has the least (since vRam on GPUs downclocks to the lowest amount of RAM if there is a difference) vRam availiable. So short of replacing your entire set of 570s with high vRam GPUs, you won't be able to solve your bandwidth problem.
In hindsight this was something I should know having remembered reading about it Oh well time to save ad plan for the next new thing
I actually have in m,y desk draw an original Ageia BFG PhysX card lol I bet it wouldnt even run physx now lol
<Dig's into his old parts box> I wonder if Windows 7 will run on a PIII 300 I'd keep it I'm hoping my stash of 10+ years old working hardware will eventually be worth something
