Depending on the load, a .30-06 has a power factor of about 400, but 12-gauge slugs can reach the 700s with ease.

If you really want to put the hurt on something, like a big critter, a 12-gauge slug does that. And here I will be speaking only of the 12-gauge variety, because while the 20 can come close, the rest … meh. The 16-gauge is so rare that it might not even exist, and 28 and .410 slugs are pointless.