In terms of efficiency and power draw most psu have the best efficiency@ or around the%50 mark leaving room for v spikes & thermal influence inside your case.  Saying 850 @ the rail. But ask yourself what amperage do you need on the specific cale/s and is it on a sing!e rail This is where longevity comes in Idle along at 55 or run that puppy wide open.? System max draw is how many watts and amperage draw. Now what do you need for that %50? Just thoughts to ponder on an old thread