Very informative thread, thanks guys.

I saw all your good feedbacks about riserless motherboards so I purchased 2 Onda 6 GPU boards from Alibaba. They work like a charm but i'm struggling keeping them inside a closed case with a low CFM fans, GPUs are heating too much.

I tried to use some spare Deltas 252 CFM fans, but I can't find in BIOS how to lower fan header voltage in order to decrease the RPM and consumption.
I don't want to keep them at 100% because of noise and don't think the motherboard can handle 3 fans at 3.9A each.

Any ideas?