From personal experience, and from the spec sheets that I've seen, most premium ILSAC GF6A 5W-30 motor oils are in fact 0W-30 motor oils (barely). There are some outliners like Valvoline EP 5W-30, with a HTHS of 3.2, but most of these 5W-30 oils have a HTHS of 2.9. What makes them not so great is their volatility. Since most of these oils don't have any Euro approvals, their volatility seems to be pretty high. In fact, Euro manufacturers either go with a 0W-20 with specific OEM approvals, or a 0W-30/5W-30 with 3.5 or higher HTHS, again, with Euro approvals.
You want 5W-30 with API SP and VW504 approval. That would Mobil 1 ESP 5W-30. Buy it a Autozone in 5 quart jugs, online, get a filter with each jug, so it comes out to about $27 per jug. You can run this oil for 5K miles easy.
If you want to stick to 0W-20, then get Castrol EDGE EP 0W-20 with MB 229.71 approval, or Mobil 1 ESP X2 0W-20 with the same approval, plus Dexos D and VW508. I mean, M1 ESP X2 0W-20 is used in the Duramax 3.0L Turbo Diesel engine, I'm sure it will do just fine in your Subaru.