Another tradeoff is between flexibility and grit retention. The adhesives
available are not as flexible as the backing to which they are attached, and
do not hold well if you're flexing a lot, which, once again, is something I
can control somewhat by not engaging in full-contact sanding, rather letting
the work come to my supported disk.

Having never been short on opinions, I would have to say this about
flexibility. It is extrememly important in power sanding and
woodturning because a simple catch or unrulely natural edge will kink
it and remove the abrasive from the backing. Try this simple test,
take a low to middle grit, 120 or 180 and fold it and roll it between
your fingers. Does it flake off of the backing or allow you to crease
and tear the paper?

I guess I'm a lot less concerned about mesh tolerance than you. Most folks
I've found who have the scratch in smooth syndrome have done one of two
things - burnished (case-hardened) the surface with heat before sanding the
last grade's scratches out, or they didn't wipe between grits, and are still
kicking loose chunks of the last around with the current.

The mesh is not as important as long as you know the grit system they
use. If they use the "P" system (or any other) fine, you have your
baseline.

Steve Worcester
www.turningwood.com