Gave the j58 a test run yesterday. Besides the instantly noticeable warmth like solographik mentioned, the other remarkable surprise is that the 2 superior pockets are incredibly voluminous. Deep pocket style.
Grabbed the j58 to mostly wear as a stand alone jacket since I loved the simple aesthetic. For that reason, I dislike how elasticized it is at the waist. When zipped, its easy for that elasticity to make the jacket ride up and give you that poofy "beer belly" look. I would much prefer a speedlock option or even a button fastening cinch similar to whats on the sleeve. But overall, this jacket just feels remarkably good when you slip it on. Its super light but the material gives it a pleasant density at the same time.