I don't get too excited about rubs unless I see them on trees the diameter of my calf or bigger. If a buck is tackling trees of that size there is a good chance he has some size to him.
I can guarantee that during the "peak" rut days I've seen 140"and better bucks put a marking rub on the outer edge(especially a corner) of smaller saplings/trees while looking for does because they are out of their core area. I've seen it too many times.