I too have been taught that higher TAS - faster chordwise airflow - less time subject to spanwise forces - lower ID.
However, consider this: higher TAS - more lift (at same AoA) - greater pressure differential - greater spanwise forces - higher ID.
So it would be a balance methinks. And since time subject to spanwise forces decreases in direct proportion to increasing TAS, but spanwise forces themselves are driven by pressure differential, and thus change by the square of TAS, surely higher TAS means more ID?
I await enlightenment...
And to the other issue of glider ballast, no, heavier aircraft means faster glide without range penalty. So if you want to win the glider race, you'd better carry some sand. But it also gives you less time in any patch of airspace, so you'd better be a pretty good at finding large areas of rising air that don't require tight turning.
[This message has been edited by Oktas8 (edited 05 March 2001).]