> It seems to me that the optimum curve would have an exposed depth equal to
> your depth of cut (thickness of shaving), which would depend on the wood
> species, grain nastiness, and your strength.

Hmm, I don't think so.  The depth can be varied by raising and lowering the
blade (like all planes).  The aggressiveness can also be varied by the
amount of skew that you hold the plane relative to your plane's direction.

Sure, the amount of curve affects the function of the plane (and I'm no
plane scientist).  Too sharp and the plane is acting more like a gouge and
it will balk more than it needs to when the iron is not razor-sharp.  But
too shallow and you lose some of the effectiveness.  But I don't think you'd
want to change the curve depending on your wood, because 99% of the bang
could be gotten out of changing the height of the blade or the skew of the
cut.

(Well, anyway, these are my speculation.)

-Shannon