@Dr4g0nfir3
I'm running 2x SLI 680's and they're only 2GB Cards (Which is not really enough for 4K) and TW2 probably averages around 40-50FPS at 4K.
I'd assume SLI 970's should be able to pull of at LEAST 60FPS, and I would have presumed even higher because the 970 is much stronger than a 680 and the additional VRAM.
As for TW3, if it's as demanding as TW2 was at release on current GPU's, you'll be lucky to even get 30FPS at Max/4K. For reference SLI 970's can only just pull off 30FPS/Max/4K in Crysis 3, and I assume TW3 will be even more demanding again.
@eliharel
It's usually anywhere between 25-40% more power required to achieve the same framerates at 1440p compared to 1080p, the % variance depending heavily on the engine.
Frankly I think the Image Quality difference is very obvious, just like the difference between 1440p and 4K is another obvious jump again, especially when it's a PC because you're sitting so close to your screen.
However whether it's "worth it" or not entirely depends on how much money you have to burn. We won't truly know how demanding TW3 will be until we finally see some Recommended Specs, but I doubt it'll be cheap. I think achieving Max/60FPS/1080p on a single card is going to be a struggle enough as it is and then moving to 1440p and 4K is a whole other ordeal. I personally believe you'll probably be looking at a very strong 2-way SLI setup at the
minimum to pull off 1440p/60/Max, but naturally it's all speculation of course.