I can tell you the RC version seems remarkably bug free to me .. at least on the 2 PC's I'm running it on, and nobody in the beta group has reported any problems with it
Beta testing went well, with at least all the major bugs being identified and dealt with .. as Emegra points out, this is no guarantee there won't be some minor bugs (as there always are in any software) that weren't identified but by definition that means they're not going to affect most users. .. any small bugs identified post-release will be dealt with through updates.
Peppermint 5 is certainly (IMHO) "ready" .. as you correctly suggested Peppermint don't release to a fixed schedule, it's only released when the beta group stop finding bugs, and it's considered "ready for release"
I'll never understand those distros that release to a schedule, even with known
bugs in place .. marketing men say this is a good idea but I'm not convinced, the fact that (like you suggested) a LOT of people wait for the .1 releases of those distro's seems to suggest they're wrong
IMHO, at least the LTS releases should be as bug free as possible BEFORE release .. but that's just my opinion.