I tried 2 x 650 Gold EVGA. It worked for like a day, then I ran into power issues with the risers and PSU overloading. Now I have the 650w on the motherboard and 2 risers + 3 gpu. The 750w is on 3gpu and 4 risers. TLDR I ended up with 1 x 650 and 1 x 750. No power issues anymore after 2+ days. You can probably get away with lower than 1000 watts after undervolting the GPUs.