I just bought the Browning XPO bibs to replace my old non-waterproof/non-windproof bibs.

I think this last consideration is critical. Once you get below freezing, the waterproof part may not be such a great concern (although I plan to wear my Browning bibs when the temps are in the 30's - low 40's), but wind-proof is a major concern. My old bibs were comfortable and had a great deal of insulation, but they were not wind-proof and warm air was blown out of them by a cold wind.

The XPO's are only $120 at Cabelas/Gander Mountain, they are water- and wind-proof, and they haveside zippers that go all the way to the hips. This last feature means that they do not have large cargo pockets on each side as some bibs do, but I don't need the pockets anyway: I keep my stuff in a Primos vest. The full length side zippers make them much easier to put on/take off, especially over winter boots.

I am looking forward to some good, cold weather so that I can give these bibs a work out. I also have a Cabelas Revolution Fleece pull-over that gives me a water- and wind-proof upper covering including a hood if the weather gets very bad. While the pull-over is not lined, it has room to add extra clothes underneath.

I should be good down to about 20 degrees.