I would strongly advise against System 7.5.x on any 68000 unless you have applications that explicitly require it. Most enthusiasts would say that the best OS for a 68000 is 7.1 but if you don't have a copy, System 7.0.x with Tune-up is usually good enough. Whatever you decide, have a look at Gamba's pages on downsizing System 7.5 and/or useful ad-ons: http://home.earthlink.net/~gamba2/index.html