That is certainly a bit conservative... :-) I think I'm using about 200 MB right now. I myself have a 10.2 GB harddrive and I have set up 2GB as the system partition where Workbench is installed.
It also depends on what you are going to do. If you want's a lots of fancy fonts and a lots of fancy 24 bit .png icons, it certainly takes some more place. If I where you I would use about 300-500 MB as the system partition.
/Jörgen
