You only need to read a few pages back to discover that miners (including myself) have successfully been OC'ing S3s with mere 500W PSUs with only 2 PCIe power inputs.
Yes, I've been following this thread since the beginning. ("discover" - really? Nice.)
But I'm talking about his results and the fact that his situation with his 650 matches my experience with a wimpy 850. The QUALITY of a PSU is more important than the rating above a certain level (and 500 sounds about right for a really good high-efficiency PSU).
I'm not as concerned with the 2 PCIe inputs as I am with good PSUs. But if you have a weak one with separate weak or marginal rails, then 2 inputs per blade could very well help. My thought is that it is the "sag" the poorer powersupplies experience with a strong maintained load that is the problem.
Back in the day with AM Cubes, we had the same persnicketiness with the quality of solid, stable PSUs. I had a couple of server 750s that would each run 2 OC'd Cubes no problem at a time when folks sometimes couldn't get their Cubes to run with a single 750 (or even 850).
This is not my first rodeo, but thanks for your kind input. I stand by what I wrote, and I think he would be well-served to try better (or more) PSUs - it worked for me, and his stated symptoms match what I was seeing.