Yes, I have tried the nightly at some point, indeed I saw some improvements, but also broken stuff: - scrolling in firefox produced really weird "oscillations" that never really went away unless quitting the application. - youtube stopped working (not that i can use it reasonably otherwise) etc. I guess I should try it again one of these days.

Yeah, nightly builds are not suitable for daily use, but they do show that the same hardware and stack can deliver much better performance in the very near future.