>
>   So, we'd be led to believe that a downwards force of 10 pounds
>   during planing, not totally unrealistic, would result in a
>   downwards mouth deflection of around 20 thou, or around 1/64 inch.
>

assuming your calcaulations and reasoning is correct (I'm far to lazy to
check) it seems like you've draw the conclusion that sole flatness just
doesn't matter.  after all, no one I know, least of all me, would use a
plane that showed a 64th of daylight under the mouth (*that* lazy I'm not)
and that normal user-pressure would assure the mouth is snug up against the
work.

but then you point out that user-pressure won't deflect a smoother quite so
much.  true.  and also we're pretty much disregarding the fact the sole may
be *twisted* instead of simply concave, front-to-back.  I think the way the
plane is constructed, you've got a heavy frog tending to resist any user
pressure in the short axis of the plane (but also trying to flatten it in
that axis as well.)  this is all getting complicated.

back to the original example.  okay, you've got an gross concave surface
and user pressure holds the center flat to the work.  but how much pressure
is exerted against the work *at the mouth* after this deflection is
flattened out?  in the example given: 0.  in effect, the mouth has *no*
effect.

anyway, personally, I don't have any planes this far out of tune, so I
can't speak to how well they do or don't perform.  I have had planes with
unflat bottoms and I've tuned (flattened) them and they seem to work
better.  I haven't done this with a #8, but I've done if with a couple of
modern blocks and have found them vastly improved.

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