If anyone interested regular KB deals as much damage as is written on it, while Pisorf does a little less.
Pisorf deals 60% of you base to a monster if you push it into a wall, or 48% (not 50%) if it hits a monster. They always take equal damage.
The monster you target can reduce the damage of Pisorf with phys resistance, the other guy cannot. It fully hurts even physical immune guys. It means that anytime you see a monster with more than 20% PR, you're better off using indirect KB than slamming him through walls.
Next time I'll look up some corrosion antics if anyone is interested.