Ted, I trotted part of this course last winter and felt that being tall was more advantageous going thru the thigh high under brush and climbing over downed logs.
I don't remember much thigh high stuff. It wasn't like running through blueberry bushes. There were a lot of the holly trees which you have to duck under the branches to get through. I do remember a lot of saplings areas where the branches were right at face level. It was so thick at there that it was impossible to read the map/compass while running as I was afraid I would run into something.
I do recall a few sections where being tall helped to get over the down trees but these were very few and because I wasn't running I guess that I felt everyone was going equally slow so there wasn't an advantage.