Sorry for asking thus dumb question, but why don't you release patches to upgrade between those betas and RCs? I have a site that runs on 6.1b2 (not a production site, of course, just a site) and there were bugs indeed; and I certainly would like to _upgrade_ this site to the new version - but there is no way!
Unfortunately we do not have time to publish all these patches due to intense work on this major release. We warned everyone - do not use these beta and RC versions on live sites.