I would disagree in regards to the amount of volume on the Viper, it is a big boat and ideal for double handers, I think in single handed mode its a fat boy and a bit too much volume but that is a personal observation and as I haven't had the opportunity to sail one, merely that of an observation.

Volume, beam and sail area are very relative to how fast a boat goes, particularly upwind. This was demonstrated on the water to me by the Shadows at Rutland over the weekend. The Shadow is a smaller boat volume wise to the Stealth, has a smaller sail area and smaller beam and yet in the stronger breeze they were more than capable of matching the F16's upwind. Some where in that mix of volume, beam and sail area ( dependant on wind strength of course ) we get an ideal water line displacement which achieves good speed. I suspect the A Class's are getting into that zone.