Doesn't the PS3 have horrible frame rate issues (when compared with 360)?
Yes and no. "Yes" when developers fail to take advantage of the PS3s "quirky" CELL processor (which, granted, happens pretty often because it's notoriously difficult to develop for.) "No" when they get to grips with it.
Generally speaking, PS3 versions of multiplatform games tend to suffer from frame rate issues due to not enough time being spent optimizing them for the PS3s peculiar architecture. This is one of the reasons why I own both a PS3 and an Xbox 360. I usually buy the XBOX 360 versions of multi-platform games that I'm interested in (like Assassin's Creed).