Mick, the answer to your question depends on many variable factors. Each jib is designed so that it is efficient within a certain range of windspeeds. The problem is that the wind doesn't always cooperate by blowing steadily within that windspeed range. Wind blows in puffs and lulls. One moment you may be overpowered while beating to windward, and then you sail into a lull, and you may wish you had more sail area. When you're racing, you select the biggest sail your boat can carry the most efficiently for the highest percentage of the time. You accept the likelihood that the boat will occasionally be overpowered for brief periods of time during the strongest puffs, but those overpowering puffs might only be a problem 4-5% of the time. The rest of the time, the sail area will be just right for the ambient wind, or you'll be sailing off the wind.
The sail trimming techniques that you're talking about can help extend the useful windspeed range of a jib a little bit, through short-lived puffs, but if the puffs are stronger, or longer-lived, there is a point where you're better off to reduce sail area. Other factors to consider are the length of the race, the ability of your crew to make a quick sail change, whether your boat is rigged for quick sail changes, and how much of the remaining race will be sailed to windward. If the boat is grossly overpowered, and you have a lot of windward work ahead, my inclination would be to change sails, even in a fairly short race around the buoys, because the boat will perform so much better that you may well make up the time lost in changing sails as against all the other boats that are still struggling, grossly overpowered, with the bigger sails. If the boat is only overpowered a small percent of the time, or most of the windward sailing is behind you, then my inclination is to use sail trimming techniques to keep the boat on its feet during that small percent of the time.