Last night I decided to upgrade my iPhone 3GS to iOS 6.0 without waiting for reports on performance. Almost every update has caused battery drain issues, but I am pleased to find that this has not been an issue this time. Battery drain seems comparable to iOS 5.1.1. I have not noticed any speed issues either, on the contrary, ithe GUI seems much snappier than before. It makes me remember a time when 3GS was the fastest iPhone ever. 😉
I am sure there will be issues for some, but based on my experience, I’d say go for it.