magbarn, you are the only person I've seen across the entire wild, wild web reporting that *only* the Air 2 can handle iOS 9 without taking a major performance hit. If that were really true, gobs of tech reviewers and users would be reporting it. We even have posters here reporting that their Mini 4’s handle iOS 9 as well as their Air 2’s do. OTOH, I’m willing to be proven wrong if you can link to leading reviewers who have concluded that!
You reported that you reached the conclusion based upon using an iOS 9 beta! But that’s hardly the proper comparison. While you didn’t respond, I assume you closed out background apps and restarted. Or, even better, that you tested your assertion on *fresh* installs of iOS 9, with none of your apps added back in. How do you know that there wasn’t something in your settings on the Mini 4 or an app you restored to it that hadn’t been upgraded properly and was crippling performance?
I like your idea, though, of comparing the Mini 4’s and Air 2’s performance with iOS 9 in the store! I will do that as I have been in the market for a 4. However, there are problems with such store comparisons, too. Lots of junk gets added; lots of apps get opened and not closed; different i-devices get different stuff put on them, even in store demo devices! Plus, certain settings get turned off by customers, including animations, etc. and those can make a difference.
So, one has to depend upon the reviewers and user reports. If you don't have links to reviewers who say it, perhaps you have links to threads where gobs of Mini 4 users are reporting gross slowdowns with iOS 9... that would be helpful to those of us considering the Mini 4.