Hang on, what does dawnguard do to the PS3?
Dawnguard brings about the good 'ol stuttering that 1.8 did quite a good job at fixing. I really hope the memory improvements and lessening of the dragon attacks brings back performance. If i hear that 1.9 changed nothing i wont bother reinstalling DG.
Dragonborn and Hearthfire on the other hand have no issues.