It will vary from game to game and depends on resolution. If you are gaming at 1080P the CPU will probably bottleneck you a bit,
At that res a 1070 is a better deal because you just won't be using the power of the 1080. I play Diablo 3 maxed out at 1080P on a GTX 980 and it is perfectly smooth.
If you are gaming at higher res the 1080 might make sense, or if you just want a card that will last you as long as possible. I've had my 980 for around 3 years now and it's been total overkill but I've been able to max everything out on every game the whole time I've had it and still don't feel a need to upgrade.