I don't recall ever seeing an estimate of the performance loss in a
glider as a function of yaw string deflection. Does anyone know what it is?

Ultimately, I'm wondering how much attention should be paid to
deflections of, say, 1/8", 1/4", 1/2", etc., on the usual 4"-5" long yaw
string.

Without actually 'calibrating' your yawstring with a slip/skid ball
for your particular ship and installation first, I don't think such
specifically meaningful data can't really be derived, and it will vary
somewhat from ship to ship (at least type to type...) so would not be
universally applicable.

Since a straight yawstring in a turn does not mean perfect
coordination in all ships, and in fact indicates a skidding turn on
some due to crossflow effects on canopies as well as the position of
the string being forward of the C/G ( wait are you just being funny
and I took the bait, hmmm the yawstring calibration card would
be nice to have, even if it's just committed to memory.

Reread 'Circling The Holighaus Way' by Johnson for a much better
explanation than mine...
http://www.owp.us/Johnson/CirclingTheHolighausWay.pdf

-Paul