performance wise, there's still a difference. perhaps not the most noticeable but it'still there, simply because the 1080 has more CUDA cores than the 1070ti. when you talk about overclocking one, you must then assume you overclock the other. and when you overclock a 1080, alongside a 1070ti, it's still faster. And perhaps even more so than with base boost clocks, because the 1070ti for the most part overclocks about the same as the 1070 does which is at best 2Ghz but typically sits below that around 1950-1975Mhz. The 1080 on average will overclock past 2Ghz and since it has more CUDA cores, the overall performance is, in general, better.
However, that's not to say that the 1070ti won't perform fantastically. If you need to save as much money as you can, I would then recommend going with a 1070ti since it a bit cheaper.
For great performance and price, the MSI DUKE is my recommendation.
https://pcpartpicker.com/product/Yfs8TW/msi-geforce-gtx-1070-ti-8gb-duke-video-card-gtx-1070-ti-duke-8g
Depending on where you live and how much tax is, it might be cheapest to buy it from B&H, especially if you take advantage of the mail in rebate to get back $20.
Also, the MSI DUKE is an all black card with a few silver accents on the back plate making it fit in with virtually any color scheme and the logo on the side of the card lights up in RGB so you can customize it to have a color of your choosing glowing from it.