Good to see your expertise on this thread. I agree with yo 100%. I asked the dealer about going to a thicker oil, but they advised against it because this is what Subaru requires. I guess the dealer can't advise me contrary to what Subaru says, but if I go to a thicker oil and I end up with engines problems due to the thicker oil, Subaru has the right to void my warranty. I don't see how 5W-30 would give me problems, but you never know.
How would 0W-30 work? That way I would have the cold start-up 0 weight then hot temp 30 weight. I much prefer the 5W-30 idea. It's also more readily available in various brands. The question is, is the reason Subaru went with a 0W-20 tighter tolerances in the engine, smaller galleys, etc. or just plain gas mileage. If it's tigher tolerances, I'll stick with the 0W-20. If it's gas mileage, I'll use the 5W-30 and take the 1-2 mpg hit for tha sake of better engine wear.
The debate goes on.