I tried my new gpu a gigabyte gtx 1070 G1 with Xcom2 and borderlands 2 and borderlands presquel.
The GPU usage is only around 60% for those games so performance are not that good.
My guess is the drivers because they worked a lot better with my gtx 770.
Do you see worse fps compared to your gtx 770 ? If not, the games may simply be cpu limited, I also see that e.g in war thunder and some other games with my gtx 970. You also could try threaded optimizations , it can work wonders for some games, but also be bad for others…