If you're looking for a minimalist experience, try the coreCD:http://forum.sabayon.org/viewtopic.php?f=60&t=22019
I used that one on an old computer that didn't have a DVD drive. It's lightning fast and quite usable.
Sabayon may not pack as much as Ubuntu in 600 MB because it comes with all the requirements in the Portage tree (e.g. build essentials)