Not much. Why spend >$300 for a cpu that barely holds it's own with the cheapest skylake I3,A I5-6600K will an overclock will perform much better in games at$100 less.
Also, as nice as the GTX970is, I would not plan on sli.
You will win fps benchmarks but gameplay will be better with a single good card.
If you will be playing at 1080P, GTX1060 will be good.
GTX1070 will play well at 1440P.
If you will be playing fast action games at 4k, GTX1080 may do it, but at that point, you might as well spring for the new $1200 titan X pascal.
Dual gpu is not supported on all games. There is more exposure to stuttering and screen tearing.