Only a 1080 Ti can handle everything at 4k on Ultra, a 1070 you're looking at low-medium settings on a lot of recent AAA titles.
And that's the lowest I would upgrade to if I were you. A 1070 Ti is going to be a very small upgrade as it is. I would still just wait. There's no sense paying for something when its priced about 30-50% higher than MSRP for a 20% increase in performance. I love looks just as much as anyone (just look at my rig) but even for me I wouldn't pay that price for what is essentially a comparable GPU just for looks.
If I were you, I would either wait for prices to come down and get a 1080 Ti, or wait for the next gen cards.
The Volta Titan is already out if I understand that correctly. The new chips could be...