But also inefficient at low loads (<15%). An 800W PSU driving an CPU idling at 50W will probably be only 50% efficient or worse. Get a PSU to match your "idle" system, not just your "OC overload stresstest". http://www.google.co.uk/images?hl=e...UTF-8&source=og&sa=N&tab=wi&biw=1040&bih=1060 Test your idle load. Whatever it is, take 5x this number for your PSU rating. If that isnt enough for your RAID and GPUs then obviously you will need a higher wattage PSU; but be aware that at idle you are horribly inefficient. Let's do some numbers: A mainboard and GPU idling at 60W Take 5x 60W = 300W for your PSU. Oh dear, that wont cover the SLI and RAID HDDs. OK, so we need a PSU at 700W. That's fine, but be aware that at idle you will probably be at 50% efficiency or worse. Shame. So for a gaming rig, you will be inefficient most of the time you arent gaming. But for a 24/7 server or NAS rig, make sure you do the numbers to ensure low heat, high efficiency, low power bills.