What Spyderlk said, GOTTA use that lower pulley for MOST of the skidding in, the upper is for lifting onto the carrying chains.
Top links are little more than turn buckles, not rated for n thousand pounds of pull.
I have to believe that using JUST The top pulley could break a top link (even if you have many turns of thread engaged) ANYWAY if a log hangs up and you are on just that top pulley. It is ABOVE the top link, so there is a lever at work multiplying the cable pull - lower links are actually in compression
Using that top pulley for skidding raises the line far too high, two problems with that a) If/when something lets go the cable is going to whip around HIGH off the ground - think decapitation. b) It has the potential to pull the tractor over backwards, while your attention is on the logs coming in - depends on tractor size, winch capacity, drag, etc.
BTW, I think the rule of thumb is that THREE turns of a screw hold things together, after that more don't help i.e. when 3 strip the 4th goes then there is a cascade failure- the whole durned thing strips out.