The problem is mesa. I've tested both drivers on my a10-7850k, and my old a8-6600k. With fglrx I had no problem running running Mario Kart Wii at 1.5x, but when I used mesa I got around 30-35 fps at 1x. You should switch to fglrx for dolphin for now mesa just isn't ready yet.
The problem you're having with catalyst might be due to it not yet supporting kernel 3.18. Try switching to 3.16, or wait for a new catalyst to come out. There's supposed to be a new driver this week, and it might support the newer kernel versions.
The problem you're having with catalyst might be due to it not yet supporting kernel 3.18. Try switching to 3.16, or wait for a new catalyst to come out. There's supposed to be a new driver this week, and it might support the newer kernel versions.