I have an iPad 4 cellular 16gb on iOS 6 and just wondering if it would be a good time to sell it and upgrade to the Air 2, the iPad is still on the old firmware but I'm running most of my apps on old versions and new games require iOS 7+ but if I were to upgrade to iOS 9 on my 4 I would want to upgrade to the air, because my iPad is on iOS 6 it would probably sell for more money becuase it's probably classed as 'Rare' nowadays so is it a good time to upgrade, would it be worth it and is there any major upgrades/differences?