Must not be a common sight to see a 7950 3GB running into VRAM issues. Surely a poor omen for the faster 3GB GK110 and GP106 cards. On the flip side, good for users to see 970 is above 3.5GB just fine here.
Out of the benchmarks I have done lately on the 7950, in Doom, Shadow Warrior 2, ROTTR, CoD Infinite Warfare, Unity Adam Demo, CoD Modern Warfare Remastered, the 7950 showed full 3GBs of Vram usage.
With the same settings, the 970 showed a difference in vram usage, ranging from 200MBs up to a full 1GB in Unity Adam Demo.
In a captain obviously manner, I would say that it's not a good thing to be restricted by vram (or even ram for that matter). Still, it seems there is some tolerance built into game engines (or apis and windows itself), thanks to which performance does not instantly tank if you go above your system specs. Also it seems that frametimes get a hit first and framerate second. Of course there is always the option to tune down a thing or two and be fine.
Now regarding the 970, it seems that the 3.5+0.5 configuration can be manipulated so it has minimal impact on the performance. I have seen instances where it climbed up to 4GBs and it was fine ROTTR, Adam Unity Demo, CoD Black Ops III, but the vast majority of apps/games seem to prefer sitting comfortably in the 3.5GB zone.
Modern Warfare Remastered has a "Fill remaining memory" option, which when selected will push the 970 at 4GBs also. The card still seems to be working ok, but you know it's not doing any rendering on the 0.5GB space because without this option vram usage drops by 500-700MB.
