Jumpy games, Framerate problems, please help

I've recently made a new i7 build with a AsRock Extreme 4 gen 3, nvidia 560 GTX , 1TB WD caviar blue, 8 GB of GSkill ram and a coolermaster extreme power plus 700 watt.
Everything run fine at this point in time, Skyrim and Saints row 3 ran at at least 30 fps.

However, I recently changed the mobo for a gigabyte z68xp ud3r, and the gpu for a HD6870.

Since then, games have been jumpy, but it's usually unrelated to framerate. I get 70 fps in Dirt 2 and Fallout new vegas however it often "jumps" slightly while maintaining 70 fps.

On another note, Skyrim and Saints row 3, which ran fine on the 560 GTX, now have horrible framerate issues.
I've googled this and it does appear to be a common issue with ATI gpu's, but my other pc with a 6850 runs everything fine.

I think this would probably be a gpu issue but seeing as everything runs fine on a 6850 and I've just changed the mobo perhaps it could be something else?

Any help would be much appreciated.

Uninstall your old drivers and start fresh. http://www.guru3d.com/category/driversweeper/

You did it with that tool? I wouldn't trust doing it manually. This could possibly be a GPU issue, but I wouldn't expect it to work in some games but not others if there were a hardware problem.

How are your temperatures under load?

Alright, I wiped all the drivers and re-installed them, and the jumpiness seems to be gone. However, whilst playing dirt 2, my gpu got up to 75 degrees. Is this normal?

The CPU temp didn't get above 58 degrees.
The case ventilation is great, a 20cm fan at the fron, 14 cm at the top and water cooling.
However, I can't stop the water cooling from running on full, it's a corsair h60. Any ideas?
It's always running at 4300 RPM.