I am about to buy a new gaming PC and, checking for specs, I initially I was going towards the GTX 970 when I learned of the 3.5 GB issue.
As far as I understand it, as long as my game does not use more than 3.5 GB, it will run smoothly but once that limit is passed, it will slow radically as it begins to use the slower 0.5GB chunk (the numbers I have seen suggest that it would go from extremely fluid play to unplayable almost instantaneously).
Most comments seems to agree that unless I play it at 4K or use mods to load high-res textures, usually I will have no issues with that.
Still, I am in doubt about upgrading towards a GTX 980; the price increase is considerable (~ 200€), the improved processing power would be welcomed but does not look like essential and, for the VRAM, the only difference is that those .5 GB are not slower.
So my question is: if I decide later to use lots of high-res textures/increase the resolution, how will the VRAM difference affect it?
Will performance degrade in a more progressive way (slowing progressively, or just losing details from the textures)?
Will the 980 behave just like the 970 (only that the 980 will have issues at 4GB instead of at 3.5GB)?
Will the game just crash if it tries to use more than 4GB of VRAM?
For me, 0.5 extra usable GB do not seem to be a lot for 200€(NVIDIA cards with 6GB are out of budget), but I may consider it if this means that the performance will degrade in a more progressive way when full.
I really do not have a favorite model for each GPU, but I have eyed this 970 (Gigabyte Gaming G1 Windforce OC) and this seems to be the equivalent 980.
Of course, if there is something wrong/not so good about those specific models I would be willing to change, I only chose the first one because it comes with the GTX 970 "preconfigured" PCs, and the second one because it was easier to compare differences with the first one.