from what i hear, most xp L1 bridges are locked, Mp's aren't. better overclocking for MP. MP officially supports SMP for running dual systems. XP is questionable, but some users say their XP's do. XP's are cheaper, and generally have higher hz, MP's are more expensive and generally have smaller hz. i think 1.2 ghz is the highest MP right now. but there are users who report up to-near 1.5 ghz MP's. both are based on the Palomino core.