Originally Posted by Farlo
Excellent... but check your mast compatibility anyway. RDM have different bend curves than SDM, much more in the bottom I think. You will keep your sail longer, and get more from it, with the proper mast (not necessarily a North). Your loft should be able to advise you.
Feeling sluggish and slow to plane is not uncommon in strong winds. Sometimes you can hardly sheet in and your board seems stuck upwind. Additionally, low speed suggests that your sail was maybe too flat (too much outhaul). I don't think it has anything to do with your boom. Raising it may help in moderate wind but many sailors would lower it in high wind anyway.
You mentioned not being able to sheet in when sailing overpowered. I use to get that a lot on raf sails but with the blocked profile of a cambered sail this isn't a problem at all.
I have a theory also that lowering the boom helps in overpowered conditions not just because of a lower body position and easier mast foot pressure, but also because with a lower boom there is more of the mast above the boom clamp (which is a pivot point) and therefore the mast can more easily bend off and exhaust gusts as the sail creates greater leverage over the pivot point.
I got a couple of photos of my overpowered session and my mast is definitely bending nicely.