Just to clarify, System 6 gets you part-way into the 68030s (though if you have an '030, you'll probably be better off with 7.1.x/7.0.1/7.5.x). I have run 7.5.4 (yes, I have a copy) on a Mac IIci, though it's quite slow to boot and sometimes takes ages to do simple things like close a window or click a button. (I have loads of software installed though.)
Also, System 7.0(.1) does not run on anything higher than a 68040. (PPC support was added in 7.1.2.) For universal-ness, I suggest System 7.5.3. It runs on almost everything (albeit sometimes slowly) from a Mac Plus (with maxed RAM and a hard drive) to a PowerBook 1400c(s)/117. Some PowerPCs (the PowerBook 1400 and systems with the "Tanzania" motherboard) won't run 7.5.5, but will run 7.5.3.
But for actual use, 7.0.1 is far better than 7.5.3 on 68000s, 68020s, and slower 68030s (though it runs OK on these if you don't have too many extensions) and 7.6 is better than 7.5.x on PowerPC as it has more native PPC code.
Just my two cents on OS advice. (NOTE: I haven't used 7.1.x or 7.6.x.)
Also, System 7.0(.1) does not run on anything higher than a 68040. (PPC support was added in 7.1.2.) For universal-ness, I suggest System 7.5.3. It runs on almost everything (albeit sometimes slowly) from a Mac Plus (with maxed RAM and a hard drive) to a PowerBook 1400c(s)/117. Some PowerPCs (the PowerBook 1400 and systems with the "Tanzania" motherboard) won't run 7.5.5, but will run 7.5.3.
But for actual use, 7.0.1 is far better than 7.5.3 on 68000s, 68020s, and slower 68030s (though it runs OK on these if you don't have too many extensions) and 7.6 is better than 7.5.x on PowerPC as it has more native PPC code.
Just my two cents on OS advice. (NOTE: I haven't used 7.1.x or 7.6.x.)