I'd prefer Panther if I could manage it as plenty of modern software still runs under it. Realistically though, Jaguar is probably the better option. I'll probably end up trying both for the hell of it so I'll see what happens.

I also had a look at the Microseconds site. They didn't seem to have any RAM listed, at least in any obvious location and their automated product request was down so I sent an email straight to their sales address. They quoted me AUD$25 bucks a piece which seems reasonable enough. I'll keep them in mind when I get back to the iMac after finishing up the G4.