Caporegime
In my own testing the majority of games will prefer a +620 clock, I can prove valley runs better with a +700 clock but it does not stress the card hard enough for it to be a valid test. I would suspect that if you run 3DMark in 1440p or higher you can also demonstrate the same behaviour I.e you can set +700 but the bench will be slower due to vram error correction.
I saw improvements going from +600 to +700 in 3dmark time spy, over on overclock.net some people have seen improvements at +800, mine locks up at that though.