I will definitely keep the PSI limit of the tire in mind. I do agree that the higher the car the higher the wind resistance can become, which could counter act any good lower RPM's I may get from taller tires, if there would be any good from it in the first place. Since I really don't have the option for testing this (As the car is not running right now so I cannot get a baseline.) Because of this I am going back to the thought of sticking with stock tire sizes for the rim and car. I figure it's a "safe" bet.
Another thought I had would be weight reduction. Lighter rims, and lighter tires. Less rotating mass can make it easier on the engine, however dropping 500 bucks on lighter rims may not pay for it self for a very long time, or even ever.
Anyone tested anything regarding lighter tires, or rims?
I have not done the testing, but I can say with confidence that a $500 investment in lighter rims will NEVER pay off, and likely could decrease your fuel economy (unless they're the same size as the old rims).
If it were me i'd go with the larger dia. tires. With the subaru's gearing you could have a potential for gains on the highway, and still have more power than you need. Additionally you'll improve your off-roading possibility, as bottoming out is the only way to get a subaru stuck.