Oh man, this is reminding me of my fix for a stuttery 30fps in the Flash Player back in the day (though I'd hang on a while command to manually force 30fps, bit of a sledgehammer but I loathe stutter).
I'm not sure if a fix to performance issues is just skipping frames, as there's no way to delay the render until the correct time...or would a timer be accurate enough... What about setting the fps to 120 but only rendering and running code when you should? Might fix the issue with 60fps being stuttery on the newer 120hz iPads...
Good grief I thought Flash's timing issues were fixed in AIR, I really don't want to fall down another rabbit hole trying to figure out yet another workaround for something so silly.