I know one thing the clamshell has to its advantage - that 60GB 7200RPM drive. That makes a huge difference in VM times and the like. I don't have Xbench or anything like that to test my machines with, so I can't provide numbers.

Another thing - does the clamshell SE have a video chipset that is accelerated under Panther? I know the early clams' video isn't, which is a big area in which the IceBooks win out.