J68WS has the weight of 444g, and 591g for J68PL. If assuming the overall construction and design does not change too much, that 147 grams of primaloft would give sufficient amount of insulation. I don't know much about insulations like professional ourdoor player so let me know if I'm wrong. Considering my personal experience on other primaloft insulation jacket, i can say that this insulation material could be very warm and light weight. So I would expect similuar peformance like j58WS. i've wear my other primaloft insulation undershell over longsleeve last winter in around 14 °F and I can have enough heat keeping inside. However considering the length of J68, as a rider jacket, I would suggest to wear a parka or longer shell to cover your waist part.