Nice elms !
I am considering clones because they will be identical genetically. Let's face it, some seedlings just root a lot better than others - we don't want to skew the test results.
I have 20 rooted Caitlin elm cuttings I am going to bare root. I could root prune all them at the same time, or not. They are all from the same parent. I will also take many cuttings from this parent plant this spring and will test them as well. Maybe I will confine my experiments to this species. I also have a big trident I could take cuttings from, I think everything tested should be clones if possible. I have one or two or three of everything, not just in great numbers, but that can be remedied. I also can take cuttings of Acer palmatum, as they are a little more difficult to root. It would be nice to use 100 clones or more, but I am limited as far as time and space. Perhaps forum members could pick a single species and work with it.
I may also purchase a dozen small Amur maple to bare root. I think I may perform a shock test by punting them around the yard after the soil is washed off. Maybe let the roots dry out a little, smash em up a bit - all in the interest of science.
I have two huge nurseries, one commercial/wholesale and one retail/wholesale near to me. They propagate and bare-root millions of plants. I may just wander over there and ask their opinion on such matters, just for fun, not drawing any conclusions but out of curiosity.