Actually it is faster than the other MW2003 (new ASUS excluded). I get better framerates on the 5555 than I do with the 2215 with PQ, emu's, PocketTV, etc.
Normal day to day operations do seem slower when compared to the 2215 but it handles the GAPI stuff just fine. Also that stupid DK.exe program still robs CPU cycles. I would recommend removing it from the startup folder to the start menu or program folder and use when needed.