https://arstechnica.com/gadgets/2017/09/ios-11-on-the-iphone-5s-slower-but-not-quite-slow/

One of my longtime pet projects has been tracking the performance of new iOS versions on the slowest hardware that can run it. I was pleasantly surprised by the iPhone 3GS and iOS 6, but after that I was in for several years of disappointments. The iPhone 4 struggled to run iOS 7 well, and the iPhone 4S only fared a little better with iOS 8 and iOS 9. Then, last year, a reprieve: iOS 10 ran pretty well on the iPhone 5 and 5C, slowing the phone down just a little but remaining totally livable in spite of it.