I don't have an A1200. I've got an A500 like the name says. It has a 33Mhz 020.
If you don't have a graphics card, I would suggest that you don't buy 3.9. I wish I never bought 3.9. I was very VERY disappointed.
Oh, and there is very little good software that requires the Reaction GUI from 3.5/3.9.