If I had a Spitfire (ex grandfathered F16) or a Viper I might feel a little hard done to accepting a box rule minimum weight. The sailplan upgrade to the 5.9 just keeps a good old design on the water for minimal cost. It is not state of the art and still has the Tornado style low profile kick up boards. It is however still a lovely boat to sail, it's even more user friendly now and it's good to mix it with the latest designs for a reasonable cost. The upgrade has been a great success and will hopefully stop the boat joining the 'dead boat society' for some time yet.
Now the weight issue, should we link this in to the F16 forum?