68000 and 68020 machines should run System 6. So should any 030 machine less than 25mhz but from 25mhz onward System 7 can run acceptably.It dismays me that System 7.x (or heaven forbid 8.x) is mentioned in the same post as a IIci.
God intended that a IIci be run under 6.x. Booting a IIci into 7 or later is like putting a sweater on your cat. Yeah, you may think it's cute, but your cat hates you for it. Trust me, your IIci hates you for making it boot into 7. System 8? It's trying its best to cut its own motherboard traces.
And 030 Macs like the IIci can't run System 8. 7.6.1 is as far as they go if they are 32 bit clean, 7.5.5 if they are not. If you are tricking it into 8 using an 040 upgrade, it's technically a Quadra now.