I FINALLY managed to update a test server using SME 8.0 to use PHP 5.5 without causing MySQL to fail after reading through some of the links here. Here is what I had to do in order to do it.
Why not apply for a Wiki account and you can then create your own page and acquire some fame
I'm sure there would be many interested and it makes it easier to find.
If you need help with formatting you could add a Document Bug and someone will undoubtedly help you (and please join in with testing/verifying or whatever else you can do to help)
As has been mentioned, there is a tough choice to be made between stability and new features. SME has a policy of tracking RHEL/CentOS and not interfering with their chosen versions. This gives us the rock solid platform that most seem to want. Unfortunately we can't please all the people all the time !
It is one of the reasons that we are pushing to get to CentOS 6 / Koozali SME 'v9' to give more up to date packages.
As has been suggested, v9 may be a better place for you to go, and it is already remarkably stable. Most of the 'bugs' are to do with additional functionality, install routines etc, but not with the main system itself. Even then, it may not be 'bleeding edge' enough for you, but may give you better long term options.
B. Rgds
John