I'm not going to pretend I'm even an armchair expert on this type of rigging, but i am a pretty good industrial rigger and we drift loads sideways all the time. I feel the need to comment, because from my training, span rigging is awesome for some stuff, but less ideal for others. The scenario you mentioned involved what to me sounds like you would have needed to drop loads onto the skyline, which because of the force multipliers involved is pretty much a no no. Even with speedline use, they recommend catching heavier pieces first, and then gently easing them onto the skyline, especially if you are controlling their decent speed.
Here's a rigging situation similar to what you had to do, and they used another tree as a rigging point to drift the limbs to a suitable landing area. They caught the limbs first, and then just eased off the rigging line while keeping the drift line taut, which will swing the limb to the landing area. This would be very easy to setup from the ground as well.
This one they didn't have a sturdy enough tree to use to drift, so they caught the piece, then lowered it down a speedline towards the base of another tree. You could do this even with a truck as an anchor if needed. I personally would feel better blocking/ rigging and controlling the forces than using a skyline under what I'm rigging out.