I am also testing WM 6.5. There are a few minor kinks I am working out, but the base OS is very stable, and does run faster. Some of the add-ons the folks threw in to increase the visual appeal are a little quirky though.
Follow this link to a more involved discussion on WM 6.5 (Now WM 6.5-Beta 4):
http://forum.ppcgeeks.com/showthread.php?t=54678