Downwind?
For all the reasons mention, we almost never sail straight downwind. On our Pacific cruise, when the wind blew directly at our destination, we usually "tacked" downwind. The only time we went straight downwind was when the wind exceeded fifteen knots. Then we usually went main-alone. As an example, when we left Mexico for the Marquessas, we were looking at almost 3000 miles, mostly downwind, after two or three days of reaching. When the fresh, 20-30K, off Mexico disappered, we were left with about 10K from the east. (If you head for your destination prematurely, you wind up dealing with the Convergence Zone for a LONG ways.) A straight run would have been limited to about 5k, provided that we could wing-out. We do not carry either a spinnaker pole or a whisker pole - too much fuss. By reaching off 20-30 degrees, we could broad-reach under full sail at 6-6.5K, tacking once a day. In winds that light, the boat stood almost straight up, with the sails steadying the boat. Straight downwind the boat would roll occasionally in swells that came from God only knows where, aggravated by the asymetry of forces due to the main sitting off to one side. My memory says that we made good an average of around 6.5K for the passage.For local sailing, in those conditions, I tend to use the jib alone, today. The HarkenII furler works so well that I can furl it easily in any conditions.