You don't really use all of your Graphics both of your DvD Drive + HDDs and your CPU at full Force. So I see there no Problem. But I know what you want to say this is just maybe the reason why there where no Issues with your Power Supply

Don't know if this is wrong or right, but it seems kinda logical doesn't it?!
Could you Test it plx?! lol
Just Install 2 Games each one on one of your HDDs and play WoW, if it's shutting down, we know it xD