I'll put some recorded video up from various games using Fraps and other means for recording in game FPS. I'm one of those using the"high resolution" in games, I have the best 1440p gaming monitor you can buy, an ROG Swift, and I have a 4k Gsync Acer monitor on my other system. I've ran games at 4k, but mostly use 1440p with both.
I have 2 eVga 970, the best/fastest 970s eVga released running SLI, and a 980 eVGA as well in the other system.
I haven't ran into a lot of this tanking performance, running games like Alien Iso, Star Citizen, Rome Total war2, CoD, CS Go, pretty much every "new" game around, and the performance with the SLI 970 system has never dumped, and in fact usually has higher FPS than my 980 system in games with decent/newer SLI profiles.
I'm interested to see if I can force my 970s into a situation where the FPS radically drops - anyone know what games and situations these complaints are about? Odds are I have the game, but googling hasn't given me a very accurate picture so far. I have a lot of different games, a wide variety of simulations, FPS, RPG, and so on, and haven't noticed any real world massive drops in any of them, and that's running with all detail settings at full blast, Gsync enabled in both systems on both monitors, one IPS 4K and one 1440p and 144hz and not IPS. Obviously there are some games where limits have been pushed to over 3.5 vram and the problem noticed, I just haven't seen it yet, and want to.
edit - It looks like Far Cry 4 and Assassins Creed are two guilty culprits, but I don't have either, and with everything maxed in Far Cry 3 I've not seen my fps tank on the 970sli system. I do have Skyrim somewhere, and apparently there are issues with it and running up/over 3.5, so I'll give it a whirl and record it and see what happens, but I don't recall it doing anything strange and having massive fps drops when I tested it with the 970s when I first installed them.
I would agree about the 980 and 4k as Ripley said, it doesn't take a lot to squash my 980 with a few of the newer games in 4k, I wouldn't have believed that 980x2 or even 3 would be necessary, but if you truly want to game at 4k and have decent playable frame rates all the time, some of these newer games pretty much require it. Sure looks good at 4k though.
This has been one of the better articles I've found so far - I really haven't found any limitations comparing my 970s vs my single 980, we play games side by side, one PC on our fiber the other on our cable connection, and it's pretty much been performance as expected with a good 25 different games. Granted, we don't have Far Cry 4 or AC U, but like this article showed, maxing out on both a 1440p and 4k Gsync'd monitors, and switching them back and forth between systems a few times - nothing has really concerned me, at full detail with anti aliasing and anti/filtering maxed out in most games.
http://www.pcper.com/news/Graphics-Cards/NVIDIA-Responds-GTX-970-35GB-Memory-IssueI haven't found any situations in any game I've tried or tested so far that I've had to avoid in order to not have my 970 equipped system plummet in performance. Max resolution with the 1440p monitor and max detail settings haven't crippled performance once for me yet, or even shown anything but much greater performance over previous 780 and 680 cards. 4k is another story, but our 980 gets smoked down into the 30s or even lower at my detail settings @4k with some games, so the same thing happening with the 970sli setup isn't surprising@4k.