For sub 14knots the best board would be a 17m edge.
Sorry! Couldnt help myself...
But seriously, rocker and width have so much more to do with efficient planing than length. (To a point).
As per eppos post, depends a hell of a lot on what you want to achieve from the board...
Ie, you wanna mow the lawn in super light?. You wanna pull flickys in 10-12, boost? Wave ride?
All very different.
I have a bunch of lightwind gear, and as far as twin tips go, my old underground 144 is pretty good. Have also ridden the 152 tahee, which was awesome upwind and still manoeuvrable.
Current fav, not tt, is the north nugget, kinda like a skim with fins...
Good luck on your quest.