Thanks RichH, I was really hoping you'd stop by.
The "more sail area" argument just wasn't holding water with me. Many new boats that have no rule limitations on design are building roachy heads into their mains. If it was truely just sail area, then they'd make the mast taller right?
Your explanation may also explain something I read in an article by Carol Hasse on small jibs whereby she was saying that if you have an extremely long luff with very little LP you end up with a lot of narrow sail at the top of the luff that does little to create lift but does a lot to induce heel.
On my boat I have a VERY low aspect mainsail (P=42, E=17), which would mean that I have a larger angle at the head of my sail than I high aspect rig. Would I benefit (in theory) from battens at the top, or is my rig low enough aspect that I already have enough sail area at the head? Is there a painful formula that I can use to figure out how much sail area should be at the head or how much roach would be idea for my sail?