True, I am still on my 980 and I didn't bump for the TI because I wanted to wait for pascal but I am starting to feel itchy and I don't think I can hold out for the 1080ti now, I might just go in on the 1080 as it will give me the extra speed I need for 1440p and like you say along with the added vram and possible DX12 gains it would be worth it for me.
I'm in the same boat. I expect that there will be a price drop on the 1080 when or shortly after 1080 ti launches (going by past trends). So you will take a bit of a hit. There will be a smaller hit on the 1070, so I'm leaning that way because I definitely want the 1080ti in the long term, but I can't wait.
Still way to early to tell because of the lack of meaningful benchmarks, but even the jump from a 670 to a 970 would have been great so even in a worst case scenario (1070 just 10-15% faster than the 970): Yes a very reasonable upgrade and a huge boost in performance.
Edit: if the 1070 is indeed faster than a Titan X, you might want to consider upgrading your CPU too. Because it will start to bottleneck you.
I think the overclocked 2x00k series should keep it fed in most scenarios without a significant performance hit.
Twice the perf of a Titan X did I hear him say?
I call bollocks.
I too doubt that it will be clearly 2x the Titan X in every scenario or on average. In VR scenarios, probably yes, in non-VR, I'm going to guess closer to 1.5 - 1.8x. Overclocked to overclocked, maybe 1.7x - 2x.
Also remember, the jump from 780 to 780 Ti (both were GK110) was much smaller than the jump from 980 to 980 Ti (GM104 to GM200).
I'm hoping GTX 1080 to 1080 Ti will be at least as much as 980 to 980 Ti, if not more, especially with 1080 Ti almost certainly using HBM2.
Because of the jump to HBM2 (from GDDR5), I think the jump will be most prominent in 4k+ scenarios and VR. At 1080p and 1440p, I wonder. Also, going forward, there will be support for higher bit-depth / HDR, which is almost like a resolution increase in terms of memory bandwidth, but I'm not sure when games start supporting that.
There wasn't a lot of coverage of the fact that it support HDMI 2.0b and DP 1.4, both of which support 4K @ 120hz. That's big (no pun intended) - I love my 1440p 144hz monitor, and have been holding off on a 4K display until they support 120hz at least, so that should be coming soon as well (maybe by next year).