Beta 4 has been super stable for me, save some weird pauses when attempting to access the Camera from apps which have already received permission. Lets hope Beta 5 fixes those.
I gave up my iOS 6 jailbreak to try iOS 7 last year... Not sure I would do the same thing this year... Good thing I have a spare device to try the beta on.
I think the beta will release today. I had beta 4 on but it was to buggy for me so hopefully beta 5 is better because I love iOS 8 especially the new keyboard and quick reply.
Honestly beta 4 is pretty stable for me. Resprings happen pretty rarely and the only nuisance I could find was Quick Reply keyboard and saving contacts in messages. Other than that I love this beta so if beta 5 is going to be even more polished, then bring it!