I couldn't get X to load with catalyst 9.10 and my 5750. Although the stream beta drivers work, so you could try them. There was also a hack mentioned by kano to disable the testing overlay relating to the stream beta drivers in another thread here. Unfortunately I only have the one monitor and can't test dual or triple head for you.
If AMD released public beta drivers, I can think of a few non-technical reasons why this could go wrong:
1) If a bug is there, it will raise undue complaints even if it's long fixed in internal builds.
2) Support - AMD will have to deal with more people wanting support for a beta driver, even if AMD takes the stance of not supporting it properly. It won't stop people trying to get support, and may slow down driver development in general.
3) Support additional: AMD will have a harder time tracking down customer problems if they're using beta builds. It's better to have defined milestone builds to help sort out problems rather than going over several beta builds with various changes to find a problem that may no longer exist.
It never happend that you got a new driver when something did not work as "full" release. Only U managed to get prerelease drivers which they only published "half", no real original installer file was available.
The problem with fglrx is that it lacks about 2-3 month behind in several aspects:
a) kernel support
b) xorg support
c) hardware support
Nv tries to fix all 3 issues with new drivers in a way it does not take so long. There you get often kernel suport even for eary rc kernels, ati thinks they are forced to wait till the kernel is stable before they are allowed to download and test it. same applies for xorg. For hardware support issues the point is that most hardware basically works, but they tend to annoy people whereever they can using watermarks. Use a beta mark in logfile or as splash, thats really enough! To remove all watermarks look there: