A Manhattan office skyscraper on Madison Avenue is up for sale, in one of the first major tests of the market for trophy office building sales this year.

John D. Rockefeller, financier Saul Steinberg and Blackstone’s Stephen Schwarzman all called the same unit at 740 Park Ave.

Kelly Killoren Bensimon, the “Real Housewives of New York” alum and top Douglas Elliman broker, has knocked down the price of her own home — which is now on the market as a $25,000-a-month rental. The ...