Battlefield One shows the i7 6700 as 22% faster than the i5 6600 with a ~2% clockspeed advantage. In order to match the i7, the i5 would need a ~20% overclock, which would bring it to ~4.7ghz, which is not achievable on all i5's - and that's just matching it. The i5 will also be drawing significantly more power at that clockspeed, possibly twice as much as the i7.
Note that both are still showing minimums fast enough for a 144hz monitor, even at stock speeds, making this, again, an academic matter at best.