"These big open worlds, which are fully interactive, do come at a severe cost on PS3. There is considerable texture pop-in and noticeable framerate issues. Playing back-to-back with the 360 version, it´s obvious that Ubisoft did not devote enough resources to the PS3 edition. The framerate is considerably worse, so much so that it begins to affect gameplay in the later levels. You can get through the first two-thirds of Assassin with the framerate being just an annoyance, but it becomes more of an issue for the final third of the missions."
http://uk.ps3.ign.com/articles/834/834770p4.html
Ces problèmes seraient certainement dus à un manque d´optimisation de la part d´ubisoft, et non à un manque de puissance de la ps3 par rapport à la xbox