Another item to consider is the life of the batteries at such low temperatures. Most extreme wintertime shooters do better with a manual wind if the mittens permit it. I have used an SQAi with an optional external AA battery pack that can be tucked under the clothing to keep them going. I wonder if such a thing exists for theSQAM?
Sounds to me you need to ask Santa for a metering prism for the ETRSi.