Apple has just stopped signing iOS 9.3.5, killing the last firmware version of iOS 9 in the process. The company has also stopped signing iOS 10.0.1 firmware, making downgrades to iOS 9.3.5 and iOS 10.0.1 impossible.
Here's a performance comparison video of iOS 10.1 beta 1 vs iOS 10.0.1 vs iOS 9.3.5 on a range of different iPhone models.
Here's a comparison between iOS 10 (10.0.1) Vs iOS 9 (9.3.5) for battery life on iPhone 6s, iPhone 6, iPhone 5s and iPhone 5.
Here's the full official changelog (also known as release notes) of iOS 10 / 10.0.1 that Apple has released today for iPhone, iPad and iPod touch devices.