I can say in one area it is at least better than TCPMP -- it has smoother playback of H.264/AAC content. I wasn't able to play the 720x480 version of the 300 trailer in TCPMP (it lagged terrible and i got roughly one frame per five seconds). Smooth as butter in CorePlayer! Using an Axim X51v w/ A12 in main memory.
Link to Frank Miller's 300 trailer :
http://images.apple.com/movies/wb/300/300-tlr1_h480.mov