I actually am on the other end... I run 7.5.5 on mine and am considering downgrading further to 7.1.2 Most likely because 6 and early 7 were the versions I used mostly back in the day.
OS 8 was the first version I had at home, so I guess it’s special for me, plus I find it interesting to see a 68k Mac running a modern OS. I feel the 540c’s ‘040 chip is quite powerful and like to give it a bit of a workout.
I’m fond of 7.5.x as well - lots of memories of it from when my parents, who worked as freelance photographers, used to take me along to different studios and agencies. I run this on my ‘030 Macs.