Looks like TweakGuides got the same results that I did in FC4, but I'm sure people will still say that isn't enough...
And I'm bolding this just to fit in with the people who like to bold random sentences!
The problem is, it's really not. I'm not saying this from a the 970 has issues perspective, I'm saying this from a proper testing perspective. He provides a video on youtube where his fps is well below 30 fps to begin with; the whole video is a stutter fest. He also provides no performance data whatsoever which makes the endeavor wholly insufficient.
With that said, I honestly don't know if any 3rd party has the proper tools right now to test for this, even fcat. Nvidia should have the right profiling tools, etc, but I doubt they'd go through the trouble. To me, there's three main problems with testing for this from a 3rd party perspective.
1) The card as designed tries to allocate everything to the first 3.5 GB section on its own if at all possible so going over that limit is more difficult than other 4 GB cards.
2) To hit the window where the resources
required are above 3.5 GB but don't completely max out the 4 GB and is playable is very difficult. It seems once you hit the 3.5 GB wall, you need ridiculous unplayable settings to begin with to make it use more and will most likely start swapping with system RAM on any 4 GB card. Even then, how much of an effect will %10 of your VRAM being slower have on game performance? That's a very difficult question to answer because as far as I know, this is the first time the question has ever come up. What about games like BF4 where the VRAM can be filled more "dynamically", will you get slightly less LOD? Will there be any effect?
3) To do a proper test you need a "clean sample" or at least expected behavior to compare against. Perhaps someone could downclock a 980 to roughly 970 performance and then compare. Even that wouldn't be exact because the architectures are in fact different, but maybe between that and a 290 for comparison, you could start to get some kind of picture as to whether or not it's a problem.
I will say that it seems like for current games, it isn't a problem, but that very well could be that for current games, 4 GB is unnecessary unless you run unplayable settings to begin with. Perhaps 970 SLI vs 980 SLI could hold some answers as well but then you run into #2 above where it is hard to find a sweet spot of memory use. Is there really a difference between a 3.5 GB and 4 GB card in today's games (again, only assuming there is a problem for testing purposes, not acknowledging one)? I doubt it. Could it be a problem in the future, who knows.
If it were me and I upgraded every couple of years, I wouldn't worry about it at all. If I wanted to keep a card for 4+ years, it would give me pause until more testing was done. What intrigues me most is the "bandwidth" test people love/hate to show. I think the biggest question there is, does it go to system RAM after 3.5 GB or is this really the second sector performance. I have never done anything in CUDA so I have no idea, but if you can get a firm answer on that, I'd say you at least have a first step in profiling the 970 VRAM performance. Sorry for the long post, I've done verification work before and that side came out a little bit.