The guy who founded Portillo's sold the company to a Boston-based private equity group a couple of years ago, for about $900 million. He retained ownership of a number of the buildings, though. A typical Portillo's has a yearly turn of over $7 million, or about twice the typical McDonalds. Chick-Fil-A also has a high average store volume, which I can believe given the lines I see in their drive-thru nearly every day. (Unfortunately, all their chicken is marinated in a garlic marinade, so my wife can't eat there.)
The Tribune had an article a while back ranking 30 non-chain Italian Beef shops. Now that's research that you can sink your teeth into!
In Chicago Al's Beef is generally considered the best of the chains, Mr. Beef is pretty good, too. (I've only been to an Al's once, I thought the beef was too greasy, maybe that wasn't representative, though.) I've seen frozen Italian Beef in stores, including Sams Club, the brand is Charlie's. It's OK, but I need to find a sturdier bun recipe, or just stick with Rotella, made in Omaha, they're not quite as good as the buns in Chicago but hold up better when dipped than my home-made ones do.