I used two SRT climbing systems, one primary, a second,a bit slack at times, as backup, plus sometimes a lanyard for positioning. One 4" diameter TIP, one 6", lower down the stem. I liked it lots. Being out on long limb walks means you're effectively not tied in twice with a lanyard and one climbing system.
I was doing end-weight reduction/ lateral reduction on 30' redwood limbs, overhanging the house. I was about 5' out a healthy 5"+ branch when it popped right off, 12" out from the collar, stripping the stub bare of bark. I have weight on my line, and some on the branch, and not bouncing, knowing redwood to be brittle.
Reminded me that end-weight reduction is a sometimes dicey, A-game affair.
Twin ropes reduces stretch, helping one maintain better loading on the lines, with less on the branch.
I used a new technique I like a lot. Could only link it
http://www.treebuzz.com/forum/threads/super-quick-3-1.32867/page-4