FPS Perf Regression on 980

At least one user has so far reported a noticeable drop in FPS from 4.6.1 to 4.7.2 in a heavy scene; using a GTX 980.

I've reproduced a perf drop in a cooked 4.7 build of elemental demo compared to the newest cooked build out of the 4.6 branch.

980 GTX Elemental Demo
4.6 (2403963): 7.82 ms
4.7 (2397709): 8.53 ms

This didn't occur on any Radeon cards or a 480 GTX. No other UE4 projects tested on the 980 showed the same potential perf regression.

Next I'm going to cook a build for the latest actual version (4.7.3) with the newest Geforce drivers available.

1. Cook Elemental for Win32
2. Collect fpschartinfo during the matinee

RESULT: lower FPS using same video driver from 4.6 to 4.7