95-96 percent usage sounds perfectly fine to me.
You don't exactly always want the GPU to be working at 99-100 percent power, you are right on the edge, and performance issues will very likely become a problem in scenes that are quite demanding.
It also comes down to the game itself aswell, some games will play alot better with SLI and some games might not even take advantage of the 2nd GPU at all.
And finally, I kinda feel that 4K is probably a bit too much for two 1070's, sure it's probably playable on lower settings but performance is surely a bit of an issue. even the new 1080 Ti, performance is only just starting to become what I would consider 'playable'.
Hope that helps a little.