wrote in message news
I'd be willing to bet the difference in torque required would be
within the limits of the torque required to lift the downward force
treating the screw as a simple inclined plane. (in other words,
insignificant).

I think the initial "breaking loose" of the screw to get it to turn requires
more down pressure and torque than does the following turns... I think back
to the days of working on motorcycles and using an impact driver that was
hit with a hammer to break Phillips head screws free as an extreme example.
A less extreme example is when I've hit the handle of the screw driver with
a hammer as I put rotational force upon it to break the screw free. More
typically I push down hard with the screw driver to break the screw free and
them use primarily rotational torque to remove them. When using a powered
driver (usually my PC drywall driver) with various bits the same dynamic
occurs... I need a lot more down pressure to break the screws loose than to
remove them.

John