Necessary? , Not right now no. with the right config a Dual core can get near i7 performance in games. Back in the day the Core 2 Duo E6850 or better yet E8400/8500 was better to have than a Core 2 Quad Fast forward roughly 7 years, almost, Now we have a number of reviews on the Pentium G3258 pitted against it's bigger brothers the i5 4690k and i7 4790k and getting similar results , Even one review Had an i7 5960X and the G3258 put up a good fight in games.
That is just games though. There is a number of good reasons to get the 8 threaded i7. and for that sweet spot the i5 takes the cake....
Note I left out AMD because obviously I am an Intel "Fanboy" ....
Seriously though It was getting to be a long reply and all over the...