Hi Bruce,
The points Wouter brings forward are correct for a "righting moment limited" situation. As long as you can hold your boat down and are not overpowered, higher board aspect ratio is less drag. The daggerboard is a small contributor to overturning moment, like 1/8th or 1/10th as important as the sail plan. A lower aspect ratio sail plan can also be faster than a high aspect ratio sail plan in "righting moment limited situations". When you are overpowered, get the CE down and the CLR up but the CE lever arm is a bigger driver.
Bill