Ron,
The cone clutch in a sail drive doesn't know that there are gears above or below it! There is no gear reduction thus no torque multiplication. The cone is in fact on a straight shaft so how is there a difference in the drive? I am certain that the two 90 degree angle turns that the drivetrain makes do not impact the torque or force on the clutch. Unless there is a gear reduction somewhere in the saildrive before the clutch the torque at the clutch is exactly what is produced by the engine! In fact the losses in the 90 degree gears are significantly less than the loss incurred by a prop shaft angled some 14 or 15 from the direction of travel. It is pretty simple engineering, the loss in the angle drive is really just friction loss (loss that is also in your "straight drive" I might add as it really is not straight but at an angle too!) Cone clutches are simple things but nowhere near as robust as clutch packs. Now I'd like not to talk about dissimilar metals below water please! Or special bottom paint, but I'd happily talk about hydrodynamic efficiency (according to Jim Taylor) or thrust vectors or SMOOOOOOTH motoring... I'd pick a saildrive any day after living with both saildrive and conventional prop shaft/strut drive.
BB