Well I drive them with 10 watts without too much trouble, but I don't listen at ear splitting levels.
To be honest I'm not too much of a PRAT believer so I couldn't say one way or the other if they do it, I would say I don't find them boring or stale in sense at all and don't feel like I'm missing anything when compared to previous so called PRAT speakers I've owned.
I would say they take a little bit more driving to achieve a satisfactory performance when compared to the ES14s, I think the small driver needs to be driven a little to get the bass moving, but it's nothing significant.
I don't think ProAc and ATC are natural competitors, size wise maybe but I wouldn't have thought they'd have too much else in common to be rivals.