Zombie Quandary

Tam posted a bit of a quandary at her blog. It makes sense, seeing as she doesn't have an AR in the vault this close to the ascension.

Now, I've got the SAKO with a couple of hundred hand tuned loads for distance work. The G3 clone when I need to 'whakka-whakka' at moderate distances. My AR is there, too, for the nitty-gritty. Plenty of pistol caliber stuff for close in along with a couple of shotties.

My question is this: Which is better for Zombie damage, steel shot, tungsten, or regular lead shot?

I've got about a thousand rounds of #6 steel shot in the garage. I also have an equal number of #7. Which one gets better penetration overall?