Assuming you have the correct viscosity, it is probably more important you have fresh oil in your engine than anything else (within limits). I run Castrol Magnatec 10W-40 in the Forrie, Penrite Synthetic 10W-50 in the WRX, each changed at 5,000km intervals. It seems to get a lot colder in the US and Europe, so in those conditions you would use a different viscosity. Similarly, if I left my cars out in the open in winter here, I would also run a different viscosity. The difference between being in the garage and outside can be as much as 10 degrees C