i look forward to hear the response of the guys who can really explain the technical aspects of your question, but from my experience i find the extra sail area on top leads to more power (not necessarily speed.. it depends how you utilize this power).

This is a great advantage in light air.. and i can handle it without to much problems up to 20knots.. above that i am rough handling my boat to keep it from capsizing and need to do everything i can to depower it (upwind) down/outhaul.. traveled out, jib furled... etc.

PS I usually solo my 5.5

I have recently acquired a pin top tornado sail that was cut for a prindle 18 (its a bit short for my rig) and i haven't had a chance to try it out.. but if all goes well... it will be my sail for heavy air (above 20)