As far as 762x39R and .30-30 WCF (Winchester Center Fire) are concerned, 39R is never going to come anywhere close to what .30-30 can do and regularly does.
The gap between these two is significantly bigger than the gap that lies between 7mm-08 and .308 Winchester. Of course, these two cartridges are vastly different from one another since they are separated by several decades and were designed for entirely different reasons. Nonetheless, the correct comparison still needs to be made.
Once again, we come back to the trusty 150gr bullet weight, except this time the Russians go full metric on us. The common soft point bullet is a 10 gram or 154 grain copper jacketed round-nosed softpoint. When fired from a twenty inch barrel, this bullet achieve a muzzle velocity of 2,104fps with 1,516ft-lbs of energy.
Meanwhile, a 150gr flat-nosed soft point fired out of a .30-30 cartridge through a standard twenty inch barrel achieves significantly better performance. This setup achieves 2,390fps and 1,903 ft-lbs at the muzzle.
As a result, (nearly) identical bullet weights and identical barrel lengths result in .30-30 going about 236fps faster and having approximately 387ft-lbs more energy. A 160gr flatnose out of .30-30 also retains nearly identical performance to a 150, but inertia means that its higher mass provides better energy retention.
The main difference between the two is their trajectory and their pressures. .30-30 has a very notable ballistic arc and starts to experience sizable drop past about 150 yards. Meanwhile, 7.62x39R, even with a round-nosed configuration bullet for hunting, shooters much flatter. It usually experiences notable drop starting out around 180 to 200 yards and eventually starts to fall like a stone around 350.
The very odd thing about this is that .30-30 has better energy transfer to the projectile and superior hunting performance with thinner case walls and about 10,000PSI less pressure per their respective CIP ratings.