Does an SLI 970 make less sense now with all this memory problems? I have 2 right now and I'm wondering if I should just return one of my 970 cause I wanted to downsample but it seems like that 3.5 barrier would cause more problems.
I have an SLI of 970s and I did some tests to see if I can see an impact on performance when they beyond that 3.5GB "barrier" :
As ACU runs at 60 FPS on my PC with everything in Ultra High and MSAA4x in 1080p (i7 5930K @ 4.6GHz and 16GB DDR4 in Quad Channel) and uses near 3.5 GB on my 970s, I tried removing the AA and use DSR to force 2880*1620 so that GPU load is still about the same (between 70 and 90%).
The result is that the game now eats between 3.7 and 3.9 GB of VRAM, and I still get pretty smooth 60 FPS even while running in Paris and looking arround. The only drops I had were when the GPUs were overloaded so it went down to 55 FPS with both GPUs load at 99%.
I played more than 30 minutes and I never encountered stutter or huge frame drops. It ran nearly as smooth as 1080p and MSAA4x (GPUs are never overloaded in this case, except in some cutscenes).
So maybe the game's engine was not using that 500 MB "slow" memory intensively, nor that "slow" bandwith is still enough for games (or some games), or my system memory and PCIE3 16x were fast enougth ?
I don't know, but for now, I won't replace my 970s as it seems to be a non-problem for me (until when ?).