THis... I don't play competitive FPS, only RPG and strategy games, and I rather have great colours of IPS. And yes, I was gaming on 120hz TN, then went to 60hz 1440p IPS, and it's really a night and day. I don't really see the difference in fluidity, but I notice much, much better colours and screen quality.
About VRAM... before it really matters, and there are more VRAM demanding games, we will be already at next architecture of 490X/Pasacal along with DX12. And then we will have single card to get 60+ steady FPS in 4K on single card.
And finally to topic of 980Ti. I do hope, it will also come with price drop of 980. I'll then get pair of 980s (hopefully used form people who switch to Ti) and will be happy gamer.
Titan (and likely 390x and 980Ti) already can do 60 steady. The benchmarks always use ULTRA/4XAA, etc. Just remove AA and you gain 20% frame rates. I've been gaming on a GTX 670 at 1080P with custom settings and get 60 steady all the time. Just because there's an ULTRA setting with AA to the max does not mean you NEED to set it there. FPS + Resolution + High is 90% of image quality. Getting another Titan/980Ti is not worth it for the final 10%, but of course, YMMV.