As the F 16HP's are "meant" to carry the spinnaker at "all times" while racing I utilized the "bouys" modification number for these suggestions.
However you bring up an interesting point- Right now the max. spi size is limited in the F 16HP class (17.5 sq m) so any boat racing "under" the F 16HP PN must use a spi of this size (in ANY race) or take an additional "hit".
However, any class legal Taipan 4.9 (since there is no "class spinnaker"- yet) can use ANY size spinnaker it wants and just apply the proper spinnaker adjustment number- Which for around the bouys would give the same numbers as I suggested but for Distance racing would involve a different number and bigger "hit". So if you have a T4.9 (Soon??) and you wanted to use the smaller spi in a distance race you would be better off racing under the F 16HP number (if it ends up being the proposed numbers) rather than the T 4.9 number adjusted for distance spinn.- Of course if there is little/no downwind/deep reaching work you'ld be better off racing as strictly as T 4.9 sloop/uni-
As for being "slower" with the smaller spi- this is still debatable and to be demonstrated in some/all conditions. The "big" (21 sq. m) spinns are the same size as the F 18 spinns and they seem "powerful" enough despite >150 lbs. more weight. I suspect there is still much to be explored in terms of optimal spinn shapes/techniques etc. on these boats- Heck, even the F 18HT's only have 20 sq m spis! And they also are "lugging" more weight than us downwind (depending on crew weight of course!)-
Sort of goes back to the whole "premise" of our boats- Efficiency versus brute Power-
