Caporegime
4 GPUs are working but things are limited by the CPU bottleneck, remember 2 x 290p @1080p should score roughly the same as 4 x 290Xs @1600p which is the case with yours and my cards. If I run @1000/1250 stock for 1600p I get over 120fps but overclocking only gets me another 3 or 4 fps.
If I was using a 4K monitor I think I could top 100fps with a reasonable overclock on the cards.
The funny part is I can get Mantle to run quadfire but DX11 refuses to run and just freezes when loading.
Post a 2x290X stock and overclocked score for 1080P and 1600P so i can compare mine thanks.
I've also found the game sometimes locks up my whole pc running the benchmark sequence and i have to hit the restart button.