Arnold Z was pretty much dead on - seedling pecans will generally take somewhere between 10-20 years to start producing nuts - grafted trees, in about half that time. With grafted trees, nut size/shape/quality are a known entity, but with seedlings, it's a genetic crap shoot - some will be better than others.
While Womack's is a good, reputable pecan nursery, I'd shy away from them as a source of grafted trees for most of MO - coming out of TX, the rootstock will be southern pecan, and may not be reliably winter-hardy for you. You'd hate to invest several years growing out grafted trees and have a particularly hard freeze kill the rootstock back to the ground(I've seen it happen), even though the grafted top was a variety that was cold-hardy enough.
Starks has a few grafted varieties - probably grown at Forrest Keeling Nursery, in Elsberry MO(look up the FKN website - they used to have a wider selection than Starks offered, and you might be as well off going right to the source.). Nolin River Nut Tree Nursery, in Upton, KY also has a good selection of northern/midwestern pecans(and other nut trees) - on northern-adapted rootstocks.
Once your MDC seedlings get established, you can graft them over to good varieties that are proven producers in your area - MU has an Agroforestry Center at New Franklin, where they're trialing a number of northern pecan & hickory selections, as well as walnuts & chestnuts - those folks can recommend proven producers, and may be able to supply scionwood for grafting.
Good luck with 'em.
