i have a 20 foot rope, when it is near the end or picking up my gun or bow i feel i am where i need to be, sometimes 17' is good other times i may need to climb to 22-25', one thing i found out very quickly when i started using the pull up rope of a known lenght, i found out that i had not been climbing as high as i thought i was, i sucked at judging height, i know most everybody else does too, cause i see guys setting 10-12 feet up and saying they were 15-20
, the only way to really know is have something that can measure it with/by, terrain will also fool you...you been given some good safety advice, take it, i have had two scary incedents several years back...start out slow and get used to your new equipment. and always utilize a safety device, your family will thank you for it