Wall Street executive John Mack and his wife, Christy, are selling their Upper East Side townhouse in New York City for $80 million. The property, purchased in 2009, has undergone extensive renovations to become a 16,000-square-foot residence. If sold at the asking price, this transaction would set a new price benchmark for townhouses in New York City. The mansion features high-end amenities, including a wellness club and separate guest quarters. The Mack’s are seeking a buyer for their lavish home in one of Manhattan’s most exclusive neighborhoods. The listing signals a continuing strong market for luxury properties in the Upper East Side.