I know I'm right on the torque variation with extensions, I turn wrenches for part time living. It also depends on what socket, extension, and length of extension. Cheaper tools and various metals used in those tools will determine as much about variation as torque range. Spot on about impact though, extensions "soften" the shock of an impact gun, negating usefulness. As I said, I'm not aware of any action that doesn't have a fairly broad range(20+ft/lb).