You should get to know the parts.
Building your own knowledge beats asking around forums. Plenty of information online.
The I5 I3 question depends purely on the game. Crysis yes i5. Cod meh won't matter.Some games will be well coded,or smaller less ai les calculations so will have no difference. Others will need the extra cores to maintain more stable fps.
I find bigger open worlds more demanding ai need more cores. But there are factors here.
Personally you are already taking the plunge. So get the I5 so you don't come across a game next year and think I should have just got the i5 . the gtx 1060 6gb (not the 3 gb) unless the price is coming too close to the 1070. Which is very possible. I'm not as sure about the American market but there is a surge in gpu prices creeping up across the board because of bitcoin mining.