In this case 14.1 is good for gaming but no good for mining. I have tried 13.12, 13.9 and am now installing 13.4 and I am still getting artifacts while mining. I also checked my other 7870 and I am having the same issues on that card as well!
I had the same problem with 14.1 and mining on both a 290x and 7950. I ended up resetting them to defaults and not overclocking. Oddly, temps went down and hashes went up. My 7950 was sitting at 550k @ 70C, but now is right around 600k @ 62C. I'm still probably going to go your route and downgrade drivers though.