I'm with James on this one.
On what do you base your statement that longboards (even with upgraded 50 cm fins)will go around an upwind/downwind formula course faster than a formula board with a 70 cm fin and a 10.0 m2 (+ = -) rig.
In lighter winds, (holey or sub planing for the formula boards) the longboard has the advantage of being able to short tack upwind to the upwind mark when the formulas cannot sail a very high course due to not being fully powered up.
As soon as the wind gets to 10 knots, the formula boards do sail a significantly longer course, but since they are traveling at 2-3 x the longboards VMG, they win easily.
At over 20 knots, it's pretty difficult to fully use the centerboard on a long board (unless you have various sizes of centerboard anyway) so the formula boards are going at least 2 x as fast upwind, and much faster downwind.
Maybe on a reaching triangular course the long boards might have a chance, but on true upwind/downwind formula type courses the formula boards are the fastest thing on the water.
Just my experience.