To porter's list I would add: Disable virtual memory, and perhaps elect not to load images automatically when browsing (or use a text-only browser, such as wannabe68k, although I am unsure if it will run on an '020-based Mac).

It sounds as if you've done as much as one can do with the original logic board. If you want better performance, you can perform one of any number of mods (including stuffing a G3 board in that compact shell). Google for Stuart Bell and Colo(u)r Classic, and you'll see just how far people have gone to upgrade the CC.