Zerobyte :
clutchc :
They both should be capable of keeping up with the 1070 Ti. The i7 would naturally be the best. What motherboard do you have?
I currently have an ASUS b250M-A Prime LGA1151 motherboard. For the two processors i was deciding over, i would need a new one.
I'd say let your budget be your guide. The slightly faster clocked 6C/12T i7 would be the way to go if you plan on keeping the build for awhile. But the 6C/6T i5 will handle any games today. A lot will depend on what your screen rez is and how much you'll want to spend on the 300-series motherboard. I presume you'll want to OC. So that means a top dollar board.
It's easy for me to tell you to get the i7 and a high-end board, but only you can decide on if you want to invest that much... and how long you'd keep it before wanting to upgrad again.