I purchased one of these Xenon SO jackets elsewhere, and bought another one here when they went on sale. The first one worked so well that I had to get another.
I mountain bike on the snow or frozen dirt after sunset in the winter. The temperature is mostly between 32F and 10F. Wearing the Xenon SO jacket and Col d'Lizárd's Swift top underneath, I never felt cold at all while I was pedaling. Just by adding one more layer of microfiber stretch shirt, I rode under 7F several times without any problem. Thus, I would say this is a great jacket in a cold weather. Just pick a good mid/under layer with right material.
As of the sizing goes, I picked a size small. I am 5'7" and 140 lbs. My chest is at 37" and the small fits me very well, giving me a snug fit around the chest, shoulders and arms. Arm length is adequately long, going over my wrist joints and some more. The back is long and it never cracks up on me. The front may be a bit on a short side, but it shouldn't be an issue, if you ride low.
All and all, I would say it's worth the money you spend on this jacket, if you are serious about riding in the cold.
And lastly, I hope Gore will bring back red/black in color next season. Their latest SO 2.0 does not carry the combination. That was another reason I rushed to get my second one while the supply of the previous model lasts.