Gamespot http://www.gamespot.com/ps3/action/assassinscreed/review.html?sid=6182795
"There are few differences between the Xbox 360 and PlayStation 3 versions. PS3 owners are blessed with a slightly more solid frame rate, although the 360 version features a little more contrast in the lighting, so it's pretty much a wash."
Ign http://ps3.ign.com/articles/834/834770p1.html
"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.
"
Are they even playing the same game LOL. This is why there should always be a demo or if anything rent first before buying.