Makes sense.  I have a Z77 board here I can test out but I don't have a CPU cooler right now. 

I tried pushing the clock a little bit (was set to auto, and it was listed as 1.2, so I assumed 1.2v is the default, pushed to 1.25..). 

Really curious as to why this works with 6 AMD GPUs and not 6 of these NVIDIA cards... :/