My wife has a 2.5 liter, 4-cyl Subaru, and a friend of hers has the big Suby 6-cylinder, both bought within 6 months of each other.
The 4-cylinder eats a quart every 2000 - 2500 miles. Been that way since new and now has 100K on the clock but it is never driven hard at all.
The 6-cylinder eats a quart every 500 - 800 miles and it, too, has been this way since new. She has learned to add oil every other gas fill-up. She also has a lead foot (her husband is even worse).
BTW: Some Subarus have the optional Electric Oil Level Sensor. You could add it and have a dash Gauge.