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.