Not a nubus power mac, but I know a Sonnet L2 cache slot upgraded Mac will work on 7.6.1.
I don't know which drivers, if any, are necessary for that generation, but that would be the kicker. I don't think I tried with 7.5.3 on my 4400, just went straight to 7.6.1. Wouldn't hurt to try, I suppose. Finding the earliest driver would be the best bet.
I say if necessary, because sometimes they're just not needed, but I might be thinking of the G3 zif upgrade for beige/b&w ... My 4400 needed a driver init