Readers of this group might like a very nice article on turn radius and
handicapping by Judah Milgram

http://skylinesoaring.org/NEWSLETTER/2005/February/

Though mostly about handicapping, it also shows very nicely why you
should not thermal at the "minimium sink speed" corresponding to the
level flight polar, but instead should usually thermal right on the
edge of a stall. (Going slower means you can achieve the same turn
radius with a lower bank angle.)

John Cochrane

BB