I have to go with 7.6(.1) for '030 Macs and 8.1 for '040 Macs. I remember the nightmare of 7.5 on my Performa 460 (33MHz LC III), and I have no desire to repeat that. On the other hand, all my 68k Macs are 32-bit clean. For PPC Macs, I generally run the highest OS that will fit in the installed RAM comfortably, and that's never any flavor of System 7. 7.x just drives me nuts with it's infuriating lack of multithreading in the Finder and the need to click and hold on menu items (a real pain in the butt for PowerBooks), among other problems.

Peace,
drew
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Power to the PowerPC!