I had amazingly good results last year wearing the mittens with glove liners. I sized up one size and carried two sets of liners, wearing one or both depending on conditions. I was in chemo last year and extremely sensitive to temps going too low or sweating, so I was really focused on it. Paying attention and adjusting early was key, but doing that I never had a problem staying warm enough. Only issue I had was overheating with chemical hand warmers. I don't remember temps, but I got out on a few really good/light days so I'm sure this saw single digits. The breathability of this setup is hudgely important, too.
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