Well officially there was only one beta and that was Build 7000, the others where all leaked builds and it's quite normal for an OS to have many builds. RC is close to RTM thus almost feature complete so I seriously doubt they will add something big by now.
Unless they do a 7 Development Reset xD (and continue where they left off with the old Longhorn..... yeah one can dream....)
Quote:It’s been confirmed that Windows 7 Build 7100 is the official RC release. Complied on 21 April 2009 it is tagged as 7100.0.winmain_win7rc .090421-1700. More recent internal builds have been released, but 7100 is the official RC build.
The Windows 7 Release Candidate will be available for download on May 5th, although expect it to be leaked before then particualarly as MSDN and Technet subscribers will get it beforehand. Already fake torrents have been seen in the wild.
Builds 71XX will be based on RC1, and RC2 builds expected around August 2009 will be Builds 72XX. Given the pace of Windows 7’s development, if I were a betting man, I would put money in on the Windows 7 Release Date being before Christmas 2009.