First, neither of these rounds are "AP".  Both rounds are capable of penetrating some types of soft body armor, but that's not what AP means (despite constant confusion in the media).  AP means Armor Piercing, and the armor being referred to is metal armor plate, at a *minimum* of 1/4" thick, and usually thicker, which neither round can penetrate.

Several 5.7mm loads can penetrate up to Level IIIA vests.  7.62x25mm can penetrate Level II, and possibliy Level IIIA vests if the velocity is high enough, and the required velocity is lower with the Eastern Bloc steel-core ammo.

But that's not the whole story.  The 5.7mm round makes wounds in flesh that are in .22LR/.22Mag class.  Penetration is FAR too shallow, and tissue damage is relatively minor.  7.62x25mm is better, but still less than a 9mm FMJ, unless you use a (fairly rare) hollowpoint, which will likely not meet the penetration goal of at least 12".

While either cartridge is capable of inflicting a mortal wound, neither is likely to STOP (read: cause near-instant incapacitation) of an attacker.  This means that, while the bad guy may die 5 minutes, an  hour, or several days later, he may well have been able to continue his attack on you despite being shot.  What we look for in load selection is a round that will incapaciate an attacker, so that he can't wound or kill you.

The 5.7mm round has had several notable failures to stop in domestic police use, from both the P90 and the Five-seveN pistol.  We can easily predict (and experience bears out) that the P90's ability to spray 5-10 round bursts into someone means that the gun can be effective even though individual rounds are less so.  But the Five-seveN is a semi-auto pistol, and also has a shorter barrel, further reducing velocity.  It has BIG problems as a defensive gun, and there are several lawsuits from individual officers who had been issued Five-seveN's as duty weapons regarding these failures to stop.

Ballistics expert and researcher Dr. Gary Roberts recommends in the strongest possible way against the adoption of 5.7mm weapons for police use, due to the inferior performance of the ammunition.

Just something to think about.

-Troy

Well, sure, if you can consistantly hit someone in the tear duct at 40 yards, then the Five-seveN will probably be a fine handgun for you.  If not...  

-Troy

Too shallow if you're using a JHP bullet in the 7.62x25mm (and that's just a guess, based on experience and examination of the one JHP bullet I'm aware of).  Certainly, a FMJ will have WAY excessive penetration in most cases, just like 9mm FMJ, but it will do a bit less damage due to the smaller diameter.  If either round hits a major bone, then things can be different, with bone fragments flying everywhere.

-Troy

Yup.  That's what I load for my CZ-52.  Of course, it's FAR from my primary handgun.

-Troy