Last month Forbes published a story ranking NYC as the 8th most-stressed city in America, behind Dallas (#7), Tampa (#4), and Las Vegas (#1). Now along comes Portfolio.com with a study that lists NYC as the 6th most-stressed, bested by Detroit (#1), L.A. (#2), Cleveland (#3), and Riverside, California (#4). (What's wrong with sunny Riverside? They've got a 14.4% unemployment rate, and