I'd say that with the dried out ones, it's about 20 to 30 degrees back lean where the doubts start to creep through your mind. The majority of trees, limb weight is not much a factor, there being no water in them, and often they have already dropped or might be ready to.
People are lucky here that typhoons usually don't pass directly through this particular area.


Tie a log midline on the pull line. It will continue to pull toward the lay, until the log hits the ground.
How far away from a vehicle can it be? Multiple ropes connected with redirect blocks? How big of trees?
Can you rent a machine of any sort?
What is your local population like, out of curiousity?
P.S.
This weight in the middle of the pull line may be in Fundementals of General Treework. My copy is out on loan.
I saw a video of someone doing it a long time ago.