+1 - 2 Day Acat regatta a couple weekends ago, first day I was going upwind as fast or faster than anyone, only to get my clock completely cleaned downwind (3 or 4 boats per leg). Moved the mast forward 1 pin for day two and was able to mostly hold my position downwind (always somewhat of a challenge since I'm 215#) in spite of usually deadly (to me) light air. I think optimum rake is a very situation and boat specific thing... more is not always better.
A-class cats with their highly efficient and very vertical masts would disagree with the vortex theory.
Scarecrow's explanation is as technical as needed for improving upwind performance. The trick is finding the right balance for fastest times around the course. Balance of lift to drag as well as upwind and downwind performance.
