There is more than slowdown to worry about with the 360 release. Nasty glitch with regard to Online Coop. When you join a game your save data is reset and then overwritten with your data from that play session. Just lost a bunch of progress thanks to this. Apparently this glitch was present in the Japanese Ps3 release but eventually patched out. Pretty inexcusable for it to be present in the 360 port.
I don't know if this happens every time, but I tested it twice and it happened both times. I should have known something was up when it reset my camera settings...