iPhone 4S, 5, and 5C do not have Metal. Metal is exclusive to A7 and above devices. They might not be much smoother, in other words.
Apple said there were general improvements under the hood and to the framework of iOS, so performance improvements should be seen on older devices as well, maybe just to a lesser extent, unfortunately. On the bright side, it still should be better than iOS 8.
Yes, many situations are smoother on iPad 2 (A5) than the iPad Air, iPad mini 2, and iPad mini 3. Control center on the lock screen and over a keyboard for example is perfectly fine on iPad 2, but it stutters on the A7 devices. This is due to the translucency effects that the newer devices have. Not sure how iPad 4 is compared to iPad Air because I never used iPad 4.
I think that Metal will make A7 and A8 devices run like they should have been running since iOS 8. From what I've heard people say, A6 devices run fine due to their 1GB of RAM and 32-bit cpu, and I'm guessing A5 devices will run slightly better on iOS 9 but not much.
Some say that Metal is already enabled but I ve never seen this in any ios 9 beta release notes.
Wasn't Metal enabled in El Cap beta 2 or something? So did Apple say that Metal is enabled in the OS X El Capitan release notes? If Metal hasn't been mentioned in the release notes yet for iOS but it was for OS X, that's a good sign it will be enabled in GM.
That's the question that kills me, is or not mentioned in El Cap beta 2 release notes that Metal is enabled? Because I didn t see this mention in ios 9.
I have the opposite feeling. It can't be worse than what iOS 8 was at the beginning.
iOS 9 is still in beta, so it's understandable that it not perform as well as a stable release, even with the improvements from Metal. Once iOS 9 is released, then it's fair to make comparisons.
