Two links for you to read.
http://www.southernexposure.com/isol...es-ezp-35.html
Jeff is conservative on his isolation distances since he was doing seed production for SESE at the time.
Some of the pictures are missing for this next one since Houzz bought out Garden Web, but the main information is there and you might recognize some of the names of folks who participated in doing this FAQ. This one is more geared to the home grower.
However, the SESE one describes in detail the many factors/variables involved in NCP ( natural cross pollination).
http://faq.gardenweb.com/discussions...ss-pollinating
Speaking just for myself I never saved seeds from popular varieties with lots of seed sources, rather, the ones that were hard to get seeds or new ones I was growing, with some exceptions, since it's less work to just raise plants from seed, and cheaper, as I see it.
BUT, I think anyone growing OP varieties should be required to do some fermentations, kind of like a rite of passage to qualify for being a certified OP ( open pollinated) tomato grower.
Carolyn