When an iOS device has twice the performance of its predecessor coupled with twice the RAM, then that iOS device is able to handle newer iOS versions with more stability than iOS devices with less performance bumps and no RAM increases. For example, the iPhone 3GS was known for its reliability, even with newer iOS versions (because it was the first to double performance and RAM). The iPhone 3G, on the other hand, was barely able to run iOS 4, all because its performance and RAM did not change from the first iPhone. Another example is the iPhone 5: more than twice the performance of the iPhone 4s and twice the RAM. Remember how fast it was compared to the iPhone 4s running iOS 6? In my opinion, if the iPhone 6s has twice the performance of even the iPhone 5s and 2GB of LPDDR4 RAM, then it will be like another iPhone 3GS and iPhone 5: fast and reliable for future iOS versions.