It depends basically on the lulls. If they are fairly frequently below 6 knots the Formula will be dead in the water and lose ground very soon. If the formula can stay on the plan then it needs just a knot or two more to point and disappear upwind. Downwind the difference is less but the formula can point further off the wind. The LB will take distinctly more breeze to plane, but maintains good progress on all courses when off plane. If you've never tried that it will come as a pleasant surprise, you can beat just about any monohull upwind without even planing :-)
As the wind gets up the formula becomes physical to sail, but in the good hands the LB won't see which way it went.