I don't know, My iPad Air 1st gen with 1GB RAM seems OK to me. Everything is faster like closing apps, animation are much smoother unlike iOS 10.3.3. On iOS 11 ONLY iPhones 7 and lower get slower vs iOS 10 when launching apps. Because iOS 11 is an improvement of performance on iPad but not on iPhone. Even the iPhone 7 is slower like 1-2 seconds delay when launching apps, for example the Camera. So iOS 11 on iPad is like Running a Mac OS on it on desktop
The only downside on iOS 11 is Launching apps, it's 1-2 seconds delay to wait for app to be fully loaded. And expect a huge battery drain on iPad Pro 2017 and lower, iPhone 8/X and lower.