IGN states that slowdown is a big issue on PS3 version, X360 got it too, but much less, both versions got a 9.2 though...
http://xbox360.ign.com/articles/828/828666p1.html
http://ps3.ign.com/articles/828/828327p1.html
I can't believe I sold my 360 and bought a PS3 just for this shit...