Something interesting about the 5.7 ammunition; what is currently available from the manufacturer to civilians really isn't good for much other than punching paper or small game.
A company called Elite Ammunition has been making some headway on that issue. Here is a link to their forums, specifically a thread covering some tests they have done:
http://www.fivesevenforum.com/viewtopic.php?f=8&t=1502
There they mention that one of their new production ammunitions is getting a muzzle velocity of 2600fps from the fiveseven pistol.
Perhaps this will allow the round to gain some more traction if they can get their supply issues cleared up.