I am glad you had a good trip and got some hands-on single-handed experience with a light air sail. You must be in Fort Lauderdale to be using Nance and Underwood. Bob sailed into some degree of sailing fame with my friend Andy Wall back in the day. I just finished an excellent book by their third sailing companion, Des Kearns (Beyond Boundaries). Their sailing accomplishments equal in some measure the accolades that many of the “household known” names that were our heroes in cruising when we were starting out, but somehow word never got out. Probably because they were not authors at the time and moved on to other things. But if you can get Bob talking…
Back to sails, I am a bit confused. You report you had an asym of 153%. My experience is that asyms are measured by area (square feet, square meter etc.) and that headsails are measured by percentage. 153% is a big genoa, but certainly not unheard of, but would usually be on a roller furler and not in a sock. Then there is always one of the variously called “cruising chutes” which are sometimes flown with a sock and I am unsure how they are measured.
I have no personal experience with a code zero, but have the sense that the term encompasses a wide range of sail design, often trying to encompass the boundary between a big genoa and an asym. What sometimes occurs is that it disappoints a bit at both. Since it is fixed at the bow, it is unable to fly free in front of the boat and may need (or benefit from) a pole to keep it from collapsing. It may however do well in light air going to wind, but is easily overwhelmed.
Take 5 knots of TW, add 4kn of boat speed and you have ~~8kn AW: perfect perhaps for a code zero. Bump that to 7-8kn TW and 6 kn BS and you have ~~12 kn AW. You will need a pretty heavy sail to tolerate 11kn AW going upwind and that is a pretty narrow window of usage. This probably means Dacron or exotic.
When going downwind the wind range expands as one can carry many DW sails into the mid to high teens (DDW at 15kn TW and 6kn BS = 11kn AW). Beam reach TW and AW are the same.
Just thinking and I welcome field reports on code zeros or other ways of looking at my thinking above.
My best, Dick Stevenson, s/v Alchemy