Ah ... excellent suggestion. It's a GTX460, and I have skipped the more recent driver updates.
Will continue to chase it. Have a second 460, and may drop both in the same machine to help tracking speed (or 1, or 2 newer cards if necessary). Thanks.

Mike

Yes! 3 failed calibrations with that original test data, then update video driver, and perfect. Reran my most recent calibration attempt from today, which failed, and ... perfect ... Misdetects .19, .19, .19, .19, .21, 1.83 and Reprojection errors .87, and less. As opposed to the 30,40, and even 70% Misdetects I was seeing.
Good call!
Thank you.
Mike

Ah ... one followup question. Regarding tracking speed. With 6 cameras (my previous successful calibration), the tracking was running about 60:1 (1 minute for every second). I understand putting a second 460 in this machine would help, but not quite double the speed. I'm wondering what my expectations might be for more modern cards, or pairs of cards?

Thanks, again.

Mike

Check this table for expected processing speeds:
http://ipisoft.com/pr/GPU_speed_v_14_04.pdf
Using 2 video cards of the same model typically scales performance by a factor of 1.6.