I called Scala's once.
They sell (what they call) Sirloin Butt in 14 lb. minimum size, and you need a restaurant ID to buy it wholesale from them. So that is the ultimate answer. I'm sure there are other butcher names for Sirloin Butt -- for instance, what cut is similar in retail stores?
My friends owns a place, and he uses "Inside Round" for his beef. Again, this is a commercial cut. He says it comes in a 25 lb. chunk, and then he fabricates it into smaller cuts to roast.
For home use, there aren't many good options. Rump roast is totally the wrong cut and taste, imho. It doesn't slice well, and that's why it has to be string tied from the beginning. Sirloin tip roast is too soft and has weird sinews that make slicing difficult, so that definitely is the wrong cut too.
Deli roast beef is usually the Top Round roast, but it's hard to find that roast (raw) in the grocery store. So, that has left me stuck with the Bottom Round roast, which is decent, but it's somewhat tough, although it's perfect for slicing.
There you have it, I'm dying to find someone to split a 14 lb. Scala piece someday, split in 4 pieces and roast 3.5 lb. pieces.
I have a Krups slicer ($99) and they are barely worth getting. It's better than nothing, but it certainly isn't commercial grade, and it cannot get beef razor thin.
Scala's and Gonnella define Italian beef, so maybe someone else could call Scala and double-check what I have said. Scala is on Orleans St.