Well, this seems a little bit confusing, though. But the fact that you need to consider first is your vehicle allowances for engine oil. In earlier times, people used to change oil with the season. Because of not getting a clear assurance, people used 0w20 oil in winter and 5w20 or 5w30 in the summer. But nowadays, car engines are being made more advanced and fuel economical. If you are sure that your Subaru engine goes on high mileage every time and you stay in the cold areas, it would not be best to use 5w20 instead of 0w20. 0w-20 oil has the least resistance in flowing so, and it can be much thinner at high temperatures. As a result, it helps to keep the parts damage-free always, But if you use 5w-20 oil here, you may end up your vehicle having friction among the parts within months.