Oh well, I bit the bullet and bought a mac mini 1.42 ghz with os x 10.3.9.
Some games from my 5500 play ok but even Snood is jerky, and Barrack is completely unplayable [it used to play fine on a 75mhz 5200, widely regarded as a crap mac]:
Laggy: Snood, Apeiron
Unplayably slow: Barrack, Quake, Doom II, Warcraft 1
Crash on start-up: Duke Nukem3D demo, Quake2
Seemingly fine: Mars Rising, GLQuake
Love os x but very disappointed at Barrack not playing. Ambrosia's website just says more or less, well you're running in an emulator so you may well get these kinds of issues. Seem to be rather extreme issues for such an old game but there you go, I never had problems with dosbox playing anything so massive slowdowns like this are new to me - if it was a game that needed a G3 400 I wouldn't have been surprised, but something from 68k/earlyPPC days? Oh... could it be because it's 68k code running under a PPC OS running under OS X - so 2 layers of emulation?
I guess I could look for the fastest Mac that can run OS9 under OSX, although the point of this exercise was that a mac mini is tiny and saves me space.