I've been thinking of rigging an afc system on a huge oak by my house and was wondering what is the minimum breaking strength needed in your pulley? I have a hitch climber pulley rated at 5,400 lbs. and a micro pulley rated at 7,000 lbs. Are these too small for life support? BTW, if you haven't seen an afc example there is one on page 50 of "The Tree Climber's Companion". Thanks, Scott