So you are betting that 4GB of VRAM will become a bottleneck in 2.5 years or less at 1080P-1440P?
No official info is known about Fiji XT because it hasn't been officially confirmed/announced. You still went ahead and bought 980Ti SLI despite trying to come off objective/impartial for months. Ya right. No one objective does that unless you are specifically tied to a GSync monitor or need some CUDA specific software or NVidia 3D Vision gaming or you have insider info that Fiji is worse for 100% fact. That's the whole point of the discussion that you seem to be evading at all costs. You never intended to buy Fiji even if it had 8 or 16GB of HBM because you didn't even bother waiting for reviews, its price, or a confirmation of its HBM capacity.
I guarantee it if Fiji beats 980Ti in performance at 1440P and 4K, you'll have some excuses lined up how in 2018 it might run into a VRAM bottleneck. If 980Ti OC beats Fiji XT OC and they cost similarly, of course 980Ti is a better choice due to 6GB of VRAM. But we don't know any of that until Fiji PROs and Fiji XT's launch. You didn't wait, which means you never even considered buying it; that's the point.
I'm not "betting" anything, as has been explained to you (are we up to 6 times now?) it's simply not a chance I'm willing to take. If you listened even half as much as you talked you wouldn't need things repeated to frequently.
Lots of interesting products are coming within the next year or less. The two I'm interested in are DX12 and Oculus Rift and I'm not going to chance being "stuck" with a 4GB card. I'm going to absolve myself of that worry.
Fiji might very well beat the 980Ti at 4k today but I'm more concerned with performance tanking if 4GB isn't enough than I am with having a few FPS more (or less) in situations they can both handle. Again, if you did half as much listening as talking, this would have already been ingrained in to your mind.
That said, I actually canceled my Amazon order because I realized it was an impulse buy and I liked some of these aftermarket coolers and factory OC's they were achieving. The most demanding game I was playing was FC4 which I'm done with. I have AC: Unity which could certainly take advantage but I'm going to play through Uncharted 3 (PS3) and Arkham Origins (which I have no problems maxing out) first, so I can afford to wait a little while and get a more complete lay of the land.
If 390x is 4GB it's still not a contender for my next purchase. I get that you're deeply hurt by this, and it will preclude us from being friends, but you'll just need to get over it.