Catfish that eat...everything?

About four or five months ago I collected four very small (less than an
inch) baby catfish from a local pond and put them in a planted ten
gallon tank I had sitting around. After researching a bit about them I
figured out they were brown bullhead cats and will get about a foot
long in the wild - smaller than I expected but still fairly large.

So after they got big enough to not be harrassed by my cichlids (and
they had been in my tanks long enough for me to be confident they
weren't carrying anything nasty) I threw them into my big tank. They
had great fun and doubled in size in no time. Then their mouths got
bigger than some of their tank mates...

They ate all of my guppies (no big loss there, I was going to donate
them to the petshop anyway) then my last remaining tiger barb that
hadn't been eaten by the severums, then two african dwarf frogs,
several snails etc. I traded all of the remaining cichilds to the LFS
for store credit and turned my big tank into a catfish only tank.

So now I'm wondering just how far the "they eat anything" phrase might
go. I'm used to doing lots of water changes after owning a host of
destructive cichlids that were plant intolerant so I overfeed a lot so
they'll grow fast. Anyway I was looking at them today and wondering if
they can eat stuff like catfood (like friskies for instance) that I can
buy in bulk for a tenth of the price of fish food. I already know
they'll eat every kind of fish food that exists, any kind of creature
that will fit in their mouth, chicken, tuna, and earthworms.

I've noticed these guys are far more hardy than just about anything I
could buy in the petstore, and I suspect that if I don't find some bulk
amounts of food and start overfeeding soon then the biggest cat is
going to turn on his sibblings and I will have one very large cat
instead of four.

Thoughts?
-Daniel