George, I will be straight with you: I do not underwrite by cap rate, so I am not going to hand you a Chicago number I do not use.
I buy single-family in Memphis, and my screen is rent against all-in price — the 1% rule — then whether that rent carries a DSCR loan at 70-80% LTV. Here is why I would be careful with a cap rate on a 100-year-old Class C mixed building specifically: the cap rate is only as honest as the expenses under it, and century-old buildings are where expenses lie. Roof, masonry, boilers, old plumbing and electrical — if the seller's numbers carry thin repairs and no real capex, the quoted cap rate is fiction.
Price it off verified rent and your own expense load, including a heavy reserve for the building's age. If it still works, the cap rate is whatever it prints.