9.3 beta 3 on my ipt5 is much better than beta 2. Maybe a tiny bit slower than 9.2, but not enough that I can be certain it's slower (it might be my imagination)
I'm a little late in replying, but I'm on 9.3.1 on my 5, and it seems fine. No complaints here. Performs better than the first few iOS9 release versions, I think - it's my subjective perception, anyway. Seems more responsive, fewer input delays, etc. I haven't noticed any battery life decline. If anything, it seems to last a bit longer than when iOS9 was first released. I haven't actually measured it, though.