Re. comments on block temperature.
A block heater will not raise the coolant temperature to any particular (absolute) level. Your coolant temperature will be a function of the ambient temperature.
Think of putting a small space heater in an uninsulated garage on a cold winter day. Garage (internal) air temperature will rise and eventually stabilize at an equilibrium between the external temperature and the heater source. The lower the external temperature, the lower will be the internal temperature.
In short - think in terms of RELATIVE temperature INCREASE above ambient. For a given engine block, this will be a function of the heat-rise capability of the heater (i.e. heater power in watts).