My G3/233 MT (Formac G3/466, 192 MB RAM, Maxtor 40 GB 7200 rpm) not only feels faster since I installed 9.1, MacBench tested the disk at 2000+ vs. 1700 with OS 8.6. In both cases the disk was defragmented before testing, and test were run with VM and all my normal extensions on.
I guess the changes (in Process Manager or Startup Disk?) really did tighten up the code! So far I think 9.1 is the best Mac OS ever. BTW, I did a clean install from CD and have had no conflicts except for having to update Virex and Stuffit.