I had one high level match to a tree with 170,000 names in it. It took minutes to load when I clicked on it. And was impossible to navigate. How can anyone work with such a large tree? I tried just searching the names for ones that were in my tree, but no luck. I don't know how else to process it - looking through the entire list of names is not an option.
But I have had 2 positive matches (but no leaf) to trees with between 30,000-40,000 names. Both matches are multiple common ancestor matches. In both cases, I only looked at the pedigree view to find the matches.
My smallest match was to a tree with 280 names. Just happened to include the right person.
If the leaf hints ever start working for all listed matches, maybe some of these large trees will become easier to research. For now, I mostly ignore them unless a common name (other than Smith, Johnson, etc) shows up.