RE: Pros and cons of smaller sails on Formula
I had fun sailing formula for a while, and tried it with all types of sails from 6.9 to 12.5 m2. I agree with Per's observation that formula boards give you an early-planing advantage even with "normal" size sails like 8.5. But I also agree with JM that 10+ msq sails give an additional boost. There were a lot of days at my local spot where I couldn't plane with a 9.4, but I was powered up with a 10.6 or 12.0.
Ultimately I sold my formula stuff, however, for the reasons Steve C has cited. Plus I realized that I could get more consistent TOW without 10+ msq sails by using a longboard for lightwind conditions. And I have more fun racing when it's on a longboard.