Interested info. My car uses ~0.5 quart and the oil is changed every 5000 miles. The usage always starts at ~4000 miles - it doesn't use any oil from 0-4000 miles. I have used Mobil 1 5w-40 TDT, Mobil 1 10w-40 EP, Mobil 1 0w-40, and even Redline 10w-40 (multiple changes), and they all behaved the same way.

I started to think it was just the way the car was, so I went back to M1 0w-40 because it met a lot of strict manufacturer specs and Redline did not perform much better.

Amsoil is interesting...

 

I was reading that anti-drain back valves don't do much on a Subaru since the oil filter is upside down. I dunno if that's true or not.