Couple of points that have to be made.
1. Just because the round goes through the vest don't expect the bad guy to go down.
A Tokarev will penetrate a Level II vest, but after it has gone through the vest it will only penetrate 4.6 inches of ballistic gel. If your shot penetrates the vest, and then hits the sternum or a rib you are not going to do much damage.
2. You are FAR more likely to encounter an unarmored bad guy than a bad guy wearing armor. Against an unarmored bad guy, FMJ rounds from a Tokarev or a .357 Sig will be far less effective than JHP rounds from a 9mm, .40, .45 or any other major pistol caliber.
Is it really worth carrying ammo that is less effective against 99% of bad guys on the off chance you might run into the 1% of bad guys who are wearing armor?