Do a test capx, Have a layout moving a sprite every tick.
Then have another using the bullet behavior.
Add a text box on each layout and have this event to get the FPS:
System.everyTick
->Text.setText("FPS :" & FPS)
and as for the DPI, its dependent on the game its self. You need to play around with values.
what DPI are you currently using for your graphics?
The iphone 4 and 4s aswell as ipad two use a DPI of 326 for there retina display. <- Moving a sprite every tick with a DPI of this should be pretty intense!!