Quote Originally Posted by STMahlberg View Post
I run (3) HD5870's on a MSI X79A-GD45 Plus motherboard and an Intel i7 4830K chip. My whole rig is overpowered with an Ultra 1200w PSU but I have put a meter on it and it pulls 665 watts running all out. I could probably get away with running a 750w PSU.

For a breakdown the rig with (1) GPU runs at about 400 watts; the other GPU's are about 130 watts a piece. So there are a few numbers to get you started.
1200W pulling 665W is more efficient. If you dropped to a 750W PSU, you would pull more than 665W from the wall to power everything.