" iOS 9 doesn't feel like it needs a major bugfix release before we can recommend it without hesitation for every device that supports it (and we should know, we tested it on most of them)."
Actually, this is not 100% correct. iOS 9 has slowed down the performance on iPhone 6 Plus and other models too but iOS 9.1 improves on that:
http://www.ithinkdiff.com/ios-9-1-hands-on-impressions/
