I have a Sandy actually...I run at 1.35V. My old cards used more power (GTX 460 SOC's) and I run them with a heavier draw CPU (Q6600 with massive volts), 2 RAIDs (of 5 mechanical hard drives) in my secondary gaming PC on a 700W PSU. So there's definitely a lot of headroom, although both of my PSU's have decent 12V ampage. Cooling was my larger issue but the MSI 760's anyway run significantly cooler than my old 460's. Generally speaking you will want clearance for 125W (OC'd 95W CPU) + 400W (2xOC'd 760s) on the 12V rail, or 44A. My rule-of-thumb is 10% rounded-up overhead, or 49A, and some gold certified, single-rail 600W PSU's can just barely manage that, for reference.