Just installed the new AMD 14.6 driver for a modest 10-15% boost on X11(darkcoin) without changing anything else at all.
Some people were reporting up to 80% more Hash on some cards depending on the algorithm so I thought I'd give it a try!!!
Seems you can tweak setting a little more as well, so I may be able to improve more with some other tweaking.
Warning: Keep an eye on your temperatures while tweaking with this driver!
This might muck up your graphs a little

I've had some bad luck with drivers in the past so I won't be moving off 13.12 anytime soon, not for a 10% gain anyway. But I'm fully aware that my charts can't represent all possible combinations, it's more of an example of what's out there. Everyone needs to do some benchmarking and some math before deciding which pool/service to use.