[hharney]

Something to keep in mind is the rational behind the higher gross weight aircraft. In 1971 the 337 gross weight was increased to 4630 lbs but the landing weight remained at 4400 lbs. The 336 at 3900 lbs had less horsepower (190 HP) engines and the A & B model 337's lacked the full 4400 (4200 & 4300 respectively).

From Aviation Consumer article 2005:
During its years in production, the 337’s gross weight crept up, starting at 4200 pounds and eventually making it to 4630 pounds, but max landing weight was limited to 4400 pounds. (The P-337, with its 30 extra horsepower, had a takeoff weight of 4700 pounds and max landing weight of 4465 pounds.)

It was common for Cessna to increase the gross of their airplanes based on newer models until they reached a threshold for landing weight. The best useful load of any model is the normal "F" model at a published 1,935 lbs, lowest was the Turbo "D" model at 1,485 lbs. The average that most of us are familiar with is about 1,575 lbs. There are STC's that have increased the gross up to 5,200 lbs. Most of us know that these airplanes can really carry a load.