These two are why I needed the 800w PSU. Originally I was just going to put the HIS 7970 IceQ X² in, but since I had the extra 7950 lying around, I figured I would put it in this system as well. Each alone would have sufficed, but extra power always helps.
I did initially have problems with the 7970 and the motherboard, but a few BIOS tweaks, and I was all good. Right now I will leave them at stock, but I may over clock the 7950 down the line to get closer to the 7970 speeds.
I am well aware that the 7950 will slow down the 7970 in a crossfire configuration, but that is negligible.The system works well. When playing games, I can always max out settings with no problems at all.
Why not the R9 290x or R9 280X?
+João Vitor Maia as I stated in my very first post, I am just redoing my build from March 2013. I do own both the R9 290x and R9 280.