I think making a decision as to how to go forward with sails based on how N20's perform against F18's in distance racing/GT300 is wrong headed. The Gt300 is mostly close reaching. F18's do well on this point of sail against the fully cut N20 sailplans. The DPN's are setup for regualr roud the bouy W/L courses...so of course using those ratings in the 99% reachings distance race is doomed from the get go.

In my experience a well sailed N20 beats a well sailed F18 round the bouys using the current sail plans.
For distance racing perhaps a better approach is to look at other ratings systems that don't rely on course types (Texel?).