mtneer
macrumors 68040
The A8 CPU is only up to 25% faster and GPU up to 50% faster than A7. Comparatively speaking, this isn't that big of a jump from the A6 compared to previous generational jumps. It stands to reason Apple wouldn't make iOS 8 significantly harder on resources compared to iOS 7.
Many people say that they see no difference. Others say new OS on old phone is unusable. In my opinion, the truth is somewhere in the middle. The new OS does not offer anything "must have" on my older hardware anyways. And I don't want to pay that small performance penalty on every app opening, transition and click..
I am typing this on my iPad 3 running iOS 5. Transitions are as smooth as they were on day 1. Another family member upgraded their iPad 3 to iOS 7 and there is a noticeable lag in app opening, screen transitions between the two.