There's no games that I know of on A500 that need fast ram. You can't add fastram to A500 trapdoor, so in that way 500 and 600 is the same.
What they do need though is more than 512kb. Like the 500+, 600 comes with 1MB already, the maximum normal 500 can take. And then you can double that to 2MB.
For fastram upgrade 600 can take a PCMCIA card, so there is no problem.
Regarding reason for 600 existence, it was originally supposed to be A300, cheap model to replace C64, but gayle chip increased costs too much. At least it is useful as a very small A500+ type machine with internal hard drive.
