Dolphin 7 RC 3 was just released today. You can read about it and download it here:
Dolphin 7 (Hookie) RC3 is out!

It appears that Boonex has included a proper upgrade script with this release as mentioned in the above blog post. Which says it will keep site settings and data.

It also appears that we will see at least one more RC release before the stable version. You can check the status of the next release at Boonex Trac for the progress.