Carl,
Any headsail that does not have at least 75% midgirth is not considered a spinnaker by the Texel Rating. If it is not a spinnaker it counts towards sail area the same as a main and jib. To put it into perspective, a US I 20 rates 2% faster then a Euro I 20 becuase is has about 15 ft^2 more sail area in the main sail. If you added a 200 ft^2 ft hooter instead of the spinaker, the boat would probably rate 5-10% faster then a standard I 20.

It just is not worth it, the way the texel game is played.

Eric