The Winter weight is the SAE viscosity rating of the oil at 0F, while the second number is the SAE viscosity rating at 210F (i.e. full operating temperature). At a 210F operating temperature 0W-30 and 10W-30 will have the same viscosity (but different shear characteristics).
The closer your engine oil is to operating viscosity when it is started the less startup wear there will be, so theoretically the 0W oils have the advantage there, although the advantage is greatly diminished in warmer climates.
If you regularly get your engine hot (250+) then the larger concern becomes how much is the oil going to break down over time? Even some so called premium oils have been known to turn into complete garbage after 1K miles if the oil is run at high temperatures. So it is in your best interest to do your own research based on the type of driving that you do.
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