what iPhone device versions to target for physics based games? (e.g. iPhone 4?)

Any experience/advice regarding what versions of iPhone devices to target for a physics/action based game in terms of performance?  Are there developers now for example making games that will target only iPhone 4S and above, and NOT target iPhone 4 and below?  (i.e. not attempt from a performance point of view to make the game snappy on these older versions - i.e. having to put in additional time to optimize)

Note/FYI:  This specific question complements a performance related issue/question I have at: http://forums.coronalabs.com/topic/39882-performance-a-little-sluggishjerky-on-older-phones/

Hello, I have reinstalled OSX and cannot use Corona. Please deauthorize all machines =) . Thank you.

Hello, I have reinstalled OSX and cannot use Corona. Please deauthorize all machines =) . Thank you.