My personal opinion:
Dont buy an A600 these days they are overrated and overpriced, people seem to like them due to their small form factor. At the price of an A600, with very few bucks more, you can surely buy a bare A1200, which is a better gaming machine in all senses, you will have 3.0/3.1 roms by default, a 68020 cpu, 2MB chipram, AGA graphics and a numeric pad!
By the way the A1200 is smaller than the A500 as you already know. With it you can get more games to play than you would on an A600. And in the end if you wish to expand it or accelearte it, it is easier and cheaper.
PS: In an A1200 you can allways for game compatibility issues, use whdload, use TUDE or even rekick and old kickstart.