Thanks all. The two bottom support lines got stretched pretty hard when the long landed....without two I wouldn't have risked it. The whole task of dealing with that tree was always going to be about that one moment. A good result then.
The third line didn't come into play until I needed to cut/separate the log. I got 2 x 35ft logs down the hill, while the rest stayed up on the hill. The logs took a tendency to roll rather than skid down the hill, causing the ropes to take several wraps where they were tied. But, I was still able to get them undone easy enough.
There were no limbs on the bottom half of tree, as jed had guessed....so I couldn't leave stubs. We did do similar on the cedar that had grown up through the fir to about 70ft i.e. left all the branches on the log sections to create a last obstacle of sorts in front of the house....just in case.