the 4.1 beta should be at least 4.0.80 version. that overlay should be the one of the 4.1 support thread and should have the old ebuild system. 4.1 shouldn't hit portage until official release (about 1 or 2 week after release). the last i've checked that overlay had the old 4.1 alpha 1, already surpassed in quality and stability by the paludis-kde4 scm overlay. you'll just still have to check how does that overlay (the one mentioned in the 4.1 support thread) evolve and hope it works. i haven't tried it myself, but i know 2 things:
1. kde 4.1 should be much more stable than kde 4.0.x or kde4-scm versions available in portage and kde4-experimental overlay
2. i've tried it on a livecd and works fine for me, so if it doesn't really work well then maybe it's due to the overlay mantainers not doing a good work.