While I have an assortment of carbon formula booms (Maui Sails Formula, wide tail; Newer HPL with the larger diameter and wide tail, and older HPL with standard thickness and narrow tail), The greatest difference I experience is in the weight, and not so much in the stiffness or the advantage/disadvantage of the tail or body width.
Geometry is one issue, but I would like to get some feedback on stiffness as well.
Let me speculate and hopefully some better formula sailors & boom designers will contribute to the discussion.
A softer more flexible boom in a gust should shorten a bit, adding to the depth of the foil, thus increasing the power and reducing the range. I use the older HPL, which is softer than the other booms on my 11.0. This is probably a mistake since the range of the sail is pretty limited for me. 15 knots and I am getting pretty stressed, but I am also 77kg and not a great formula sailor. However, I like the lighter weight of the old HPL.
It's not likely, but would a softer boom on a deep downwind run be better in a gust, deepening the pocket and stabilizing the sail? Just a blind theory, but who knows? Upwind, it seems clear that increasing the foil depth in a gust is not a good thing, so a stiffer boom would be better.
As for boom width in the tail, a wider tail that keeps the sail from creasing over the boom when bagged seems like a good idea. In the front, I am not sure about that benefits, but I doubt that a wider boom has any impact on stability.
At what point (sail size) is the difference between the stiffness of an aluminum boom and a carbon boom become insignificant? I guess it depends on the sailor and conditions. A PWA slalom racer with a 7.6 in 30 knots could probably tell the difference. A advanced recreational sailor with a 7.6 in 20 knots probably can't. What do you think?
Formula 160; iSonic 111; HiFly Move 105; Tiga 263; '85 Mistral Superlight.
Maui Sails TR 11.0; 9.2; 8.4; 7.6; 6.6; Maui Sails Switch 6.0; 5.2; Maui Sails Global 4.5; 4.0.