It’s been a few days since I installed and starting using Emacs 27.1RC1 for all my day-to-day chores. If you follow the Emacs development list, all the items concerning 27.1 problems might lead you to think that it still wasn’t very stable but I haven’t found that to be the case at all.
By now, I’ve performed just about every one of the workflow operations that I do with Emacs and it’s performed flawlessly. The only difference I’ve seen is that Org-mode on large files is much speedier that it was before. It’s the same Org-mode so that probably means Emacs itself is faster.
I even tried EWW although I don’t usually use it much. It seemed about the same as before but I don’t have enough experience with it to say for sure. I’d really like to move as much browsing as possible into Emacs so perhaps I’ll try to use it more and get better familiar with it.
The TL;DR is that 27.1RC1 seems very stable to me, a very heavy user, and I have no hesitation in recommending that others upgrade to it. Doubtless the final version will be released soon so if you’re really wary just wait but as far as I can see there’s no reason not to start using it and help with the final testing. All you have to do if you find a problem is file a bug report, which, of course, you can do right from Emacs.