with the 970 doing an 18 and the 570 doing a 17 im pulling 500 watts at the socketthat is still a safe area with a 750 watt psu right? With a high quality PSU, you should be able to run at 100% 750/.92=815 watts at the wall.
Even an average quality unit should have no worry at 80% continuous load. 750*.8/.8= 750 watts at the wall.
general air flow to your MB VRM, cards and their VRM is a more likely issue with the continuous loads of FOLDING. If your PSU is of an average or better quality, you should have no worry unless your cat/dog has filled it with hair. ;)