I had the 815EPT Pro for a few weeks, which is virtually identical with the 815EP Pro, but supports Tualatin, and it was very stable and overclocking friendly. I had it up and running at the maximum 166 MHz FSB without problems.
But I have to admit, that it doesn't have as much OC features as the Abit and the GB(to be precise it lacks FSB over 166 MHz and that's all that makes it worse than the other two). But I think it's a good board for overclocking.