if i crossfire on my amd system a 6870 major brand with a 6870 sapphire, will that be okay. Side track real quick, is it okay to crossfire a 6870 with like a 7850? or will that crap things out? and if im crossfiriing the two 6870's if one of them is the actual major brand from AMD, and the other is from like MSI or sapphire, thats okay right? as long as its the AMD chipset?