One thing you’ll notice is that iOS 10 is noticeably slower than iOS 9.3.5 at booting up, but once it’s up and running, it’s generally as fast or faster than iOS 9.3.5 on all devices — even the aging iPhone 5, which is powered by Apple’s 4-year-old A6 processor.
iPhone 5:
iPhone 5s
iPhone 6
Unless you have another reason not to update to iOS 10, then — like you really rely on a jailbreak — this is an update you will want to get your hands on. Not only will it not slow down your device, but it brings a whole host of amazing new features.