In my neck of the woods it isn't unusual to see DAs down to -7000'. Engines make good power IF you can provide them adequate fuel, which can be a trick. How do you enrich for -7000'? Wings provide excellent lift and props make tons of thrust. In cold temps we need to turn prop speeds back to prevent excessive tip speeds. On hard packed surfaces skis are really slick so takeoff performance can be crazy good but with no brakes landing performance isn't equally rewarded. Fun stuff, at least until you sink a ski through the ice and have to wade in the water in sub zero temps. That is not so fun.