Also running a 550e @ 733. Abit, I've heard, has had ups and downs, but I've only recently had any problems with them and have used litterally DOZENS of their boards. I think the voltage regulators in the 4 KT7-Raids that I just bought are a little out of sync though. I have bunches of other BX6r2's running around with everything from C-366's and 466's, and P2's in them to P3e's! They really are a nice, stable feature filled (for thier day) board.
Joe