I know when it gets around single digits. My power steering gets stiff. Granted I keep my internal PS coolers in the radiator for this reason and just change the radiators every 10 years to prevent the milkshake scenario.
Very rarely do we get temps below 0 F for long periods time. A few days maybe a winter. One winter in 2015 it stayed at 0 degrees and below for many weeks.
I agree with others that a synthetic automatic transmission would be much better in really cold temperatures.
Bypassing the heater feature of the internal power steering will cause issues in these very cold temperatures. As this is why they put the cooler in the radiator
that will act as a heater in winter.
I really feel for our brothers and sister up in the really cold winter temperatures that can be very nasty. :-(
Hang in there a few more weeks and will be turning for warmer temperatures.