Actually it depends. For single card 970 probably it will have a hard time maintaining 60FPS even before the card reach 3.5GB usage. But with 970 SLI the config will have more raw power. I'm saying this as 660SLI owner in the past. Just like 970, 660 also have weird memory config because nvidia were going to use 2GB with 192 bit bus. That 3.5 GB on 970 probably not much of an issue even on SLI if VRAM usage does not significantly increase in some games due to new generation of console have more RAM.