"Mops" and "Sherwood Compact" are two different dwarf varieties of mugo pine(I've never heard of the variety Sherwood). From my experience, they are both very slow growing, with a very compact, bushy growth, and, generally, grafted. Google American Conifer Society and check out their database. You will find many dwarf and miniature varieties of mugo pine that have basically the same growth rate and form, though the foliage will have subtle differences in color and needle shape. I've heard people discuss them as possible material for bonsai, but have yet to see many bonsai made by any of them. Most mugo bonsai I've seen have been created from the species, and not dwarf cultivars. This isn't to say it can't be done, but I think it would be difficult developing a bonsai given the extremely slow growth rate of these trees. You would also have graft union to deal with in most cases. Good luck,
Dave