Shad Lords, who developed the 6.5 version, once wrote:
"6.5 is/was a stopgap and a proof of concept for me. It is basically Mitel's 6.0 (not 6.0.1) with latest fedoralegacy updates and samba/email upgrades. There have been updates released since then but it is still
just basically a 6.0 with updated packages. The intenance process that is pushing forward will eventually make 6.0, 6.0.1, and 6.5 identical."
So if you need a production ready version now, just use the SME 6.01 (maybe with our update script).
If you want to set up a test server, you can use SME 7 beta, which is already quite stable.