I love my FN 5.7, great gun no recoil, light and accurate.
I however would never use it for Carry or Self Defense. With the highest mussel velocity of any pistol, it will travel way to far, go right through people and keep going.
With the right ammo, (frangible or hp) That 5.7 penetrates LESS than a 357, 9mm, 10mm, 40 or 45 (all with hollowpoints) be it in drywall OR flesh
As far as highest muzzle velocity goes, There are actually MANY pistol cartridges faster than the 5.7. 224 boz and its other off shoots as well as the 5 or 6 offshoots of the 45/223 and then you have the dillon cartridges and even the 357 sig with the frangible 55 grain rounds at 2100fps out of a 5.3" glock barrel!
STILL
NOTHING stops bad guys like any frangible bullet over 1100 fps out of 38,9mm,40,10mm or 45, a 5.56 hp over 2300fps (8 inch barreled ar anyone?) or a 45 185+p golden sabre @1100 fps+.... Aw heck just carry a surbu 12 ga with 2 3/4 00buck!