I went with 3/4 and have not looked back. It did take me a bt to figure out and learn to sleep with the pad under my legs.
I also tend to be a side sleeper and as such don't need as much length as I thought I would for as tall as I am.
I have been carring a sit pad for a while now, predateing my move to the trees. So, was already thinking 3/4 when I started. I have not been down to the 20's yet s I can't say for sure on how I am going to feel at the lower temps, but down into the 40's it's all good and at about 16oz for the 3/4, I love the weight.
"When you see something wobble, push it."