I'm using ME on an M10K system, and it runs great. The only time the performance really seems to lag is if I'm browsing media in a directory that has a lot of entries. For example, I have something like 24,000 songs, and if it has to update the database, it gets real sluggy. Also, if I'm navigating to a folder with a few hundred songs or subfolders, it slows down appreciably.
Do you see the 'Busy' text a lot when changing directories? Have you set database refresh to manual?