George,
You can rely on our collective sense of humor around here, especially the cheap shot variety. The nefarious Digital Gee started a thread awhile back on Haiku. Got pretty silly.
Seriously, the foam impression method works as well or better than some others. And, yes, you want a saddle that has enough material 'left over' to fully support the sitbones and the adjacent tissue. That's why I prefer a B67/66 type for riding in a non race posture. That is, when a majority of my weight is on the saddle.
If you have ischials that are 6" apart overall, you could experience the a$$-hatchet effect on a 17. They are only 6.7" wide. Personally, I prefer more material beyond my sitbones for support.
Direct answer to your question: IMO, yes, you would be better off on a 67. Mostly because of the bike you ride and how it will distribute your weight. You will like the springs, too. Not very supple, but they do work.