Roy, you are correct. I don't run the PTO at 540 RPM, more like 375 or 400.
Might cut a bit faster at 540 but it also can cause more flying chips and stress on parts if the tree happens to lean onto the blade. A few times when cutting down stumps to ground level I've had a chunk of wood get between the top of the blade and the frame.. squeals a bit then. I added a mesh screen between the saw blade and me (the operator). Fewer chips on me.
I get more pleased with it the more I use it. With the iMatch, I can attach it, hook the PTO up, and be off cutting in a few minutes.
Cleaned the stumps off an acre of land a neighbor had cleared of small hardwood trees (making some oak savanna) and wanted to mow there. He was impressed with what could be done.