It's a valid question to most UBB™ owners who are on shared hosts. Pilot, if you can write the scripts to test like you said, I'd be happy to spit out some performance figures for 5.47e, 6.04f and (when ready for release) 6.1, it should be interesting for everyone, I have a win2k machine we can test on.
CC is working on the IO issues for 6.1 in upcoming beta's, hopefully some strides will be made there to correct them. Right now, feature-wise and code-wise, it is looking real good...:)