Performance is always a tricky thing to judge on iPhones. Look at the stats alone and most high-end Androids leave it in the dust. But use one, and it'll often feel like the fastest thing since Usain Bolt's sliced bread. The iPhone 6 is no different.
The new iPhone has an improved processor, namely the A8, and whizzes through tasks without the slightest of pauses. The previous A7 was shockingly fast thanks in part to the new 64-bit architecture that arrived on that chip, and that's obviously retained here. And while the new model doesn’t feel any faster, it has more pixels to move around and is probably doing more in the background to boot.
There’s also a new motion co-processor, the M8, not to be confused with HTC’s flagship. The co-processor now measures altitude thanks to a built-in barometer, so it can monitor when you are climbing or descending stairs. Health apps will make much of this and Apple’s own Health app has a dashboard to record your steps, cycling and more, made possible by the new hardware.