"Stopping power"? Neither is great, but the 380 is better. It has more energy and shoots a heavier bullet. But, it's no 9mm by a long shot.
NO, there is no PPK in 9mm and if you're getting a PPK, why on earth would you want a .32 over the .380???? But, I say, if you are looking at PPK size guns, do yourself a favor and look at compact 9s and compact .40s. Much more power in often a smaller, lighter, more concealable gun. They are bigger, however, than one of the small .32s or .380s like the NAA Guardian or the P3 AT or little .32 Kel Tecs. A normal jeans pocket will swallow one of the smaller .32s or .380s. The PPK is a good gun, it's just sorta bigger than it should be. It will never be built in 9mm because it's a blow back operated weapon.