Sat Nov 11, 2017 2:35 pm by bob
Well, an easy test would be to drop the number of clients so you don't get 100% GPU events, and see if that makes the problem go away. If it does, then I'd have to suggest that the graphics card is not up to snuff. If you still get black screen events with the GPU not hitting 100%, then it is more likely to be driver or power related.
edit: the large fluctuations are indicators that something is not coping, and it is requiring time to switch between processing contexts - generally loading and unloading the necessary data in order to process the next item.
also, make sure you have turned off Shadow Quality, SSAO, and any form of AA