iOS 11 pretty well crippled my iPad Air.
I have an original Air, 16 Gig with 2.5 Gig free... And an iPad Pro 9.7. Prior to iOS 11 both devices performed roughly the same. The Pro was a bit faster, but not by much.
When iOS11 came out, I installed it on the Air first to check out the new OS and get used to it before I put it on my Pro.
The upgrade wasn't an upgrade at all. The Air took a HUGE performance hit. For instance, an App splash screen that might have only appeared for a second now takes 5 to 8 seconds. When I click on the 'Settings icon and Settings opens, I get a blank screen for about 2 seconds before the settings details appear. It used to be pretty well instant.
I've rebooted it a few times and nothing seems to help. My Air is now unpleasant to use.
The performance degradation was so bad, I'm afraid to install iOS 11 on my iPad Pro. It;s still running 10.3.3
Next we hear Apple is slowing down older hardware...... Not happy.