Question
-useLegacyAOT=no big drops in performance
Here is the bugbase ticked https://bugbase.adobe.com/index.cfm?event=bug&id=3695884
There you will get sources and precompiled IPA that can be executed on any iOS device (I use my Enterprise license).
The same code with -useLegacyAOT=no on iPad4 iOS7.0.4 show >400ms testst. The same but without -useLegacyAOT=no show ~310ms
Also small notice. It's can be no true but may be issue also.
Try to compile this test for Air 3.6 and Air 4.0. I see small different. Looks like VM Math was updated 
And it's increase latency between Runtime and CPU
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