09-19-2014, 03:14 AM
mixing and matching normally isn't a problem, but in this case you're talking about mixing Overdrive5 / PowerTune 1.0 and Overdrive6 / PowerTune 2.0 cards, and at least one person has reported problems with this combination. you can likely make it work as long as you run with '--gpu-temp-disable --powertune-disable' and manually manage your cards, but sticking with 280s you shouldn't have a problem.