It's all about layering... Good base layers and socks, warm but not bulky mid-layer and then a windproof outer shell. I've been using Asio Gear for the past 3 years. Admittedly, it doesn't get cold enough here in SC for me to use their late season bib and jacket. For SC late season, I wear a medium base layer (top and bottom), Asio's mid-season pants, mid-season hoodie, Asio's Core-Warmth Vest, Asio's windproof Sherpa-lined pants and jacket, wool socks and boots with 400gr of Thinsulate. I've worn this setup in temps as low as the upper teens and have been perfectly comfortable.
While hunting in MD, I still use my Asio Gear layering system as described above but instead of the Sherpa series pants and jacket, I wear the Asio Gear late-season bibs and jacket, which are also windproof. I'll also bump up to a 1000gr Thinsulate boots. I've used this setup in single digit temps and again, have been completely comfortable.