> You really beleive that was intentional? Like there's some code there that says if running on 4S then run slow?

You:

> To spell it out - One code path is fast, one code path is slow

Intentionally designing new features for new devices and potentially screwing over old devices is _way_ different than having checks that say if (iPhone4S) { sleep(300) }

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The solution as the other poster replied is to not update your phone past 1 major version, even if apple lets you. The other solution is that Apple magically makes your processor 8x faster in a software update. At this point I don't even know what you're expecting.