I have an iPad 4 since it came out and I've tried all its upgrades, iOS 6 was great, iOS 7 was awesome, iOS 8 is bad and iOS 9 seems to be good. Apple did a huge mistake regarding releasing iOS 8, it's completely horrible. Apple planned to control iOS 8 in a new way, (slow down device --> user angry --> user fade up --> gets the newest iPad --> revenue). Apple started losing some of its fans after iOS 8, so it decided that iOS 9 would be optimized for old devices (A5 devices). Unfortunately Apple is not yet complete with optimizing the OS for middle aged devices (A6 and A7) so these devices performed some kind of more worse than older devices, what's good is that iOS 9.2 is aimed directly at the A6 and A7 devices to improve the user experience, animations and performance. Comparing iOS 9.2 beta 1 to iOS 8.4.1, Apple did fix all the annoying animations but unfortunately some other little annoying animations came up and i think apple is kinda improving (it's usable compared to iOS 9.0.2 or 9.1), iOS 8 was aweful, it was laggy and used to stutter after doing a simple task. iPad 3 is suffering with iOS 9 which kinda gives u an advantage over it. The iPad Air is just a tiny bit faster than the iPad 4 with iOS 9, so i think it's good for u to upgrade, just wait for iOS 9.2 final release, so that u won't get a bad impression of iOS 9. I hope Apple keeps on updating to fix all the bugs.