If you disable all of the ATI extensions in Classic (which aren't needed if you're running OS X) then you seem to get better performance in some Classic applications.
[Editor's note: As an expansion of this theory, there's a bunch of stuff that I've disabled in Classic - nearly everything, in fact. I basically installed just the base OS with networking, and nothing else. Then I installed (running the "Classic" 9.1 natively) all my apps that put bits into the system folder (Office98, goLive, etc.). Then I restarted into X and set my lean OS 9.1 as my Classic volume. You can definitely improve performance and decrease loading time by thinning your Classic system -- which is another argument for having your "real" OS 9.1 on another partition, so you don't have to mess around with extension sets.]

