I agree with Ken. My '02 WRX wagon has a similar weight to the STi, with a smaller, less powerful engine. I've only averaged about 18.5 miles per gallon over the last year, about 20,000 miles. Even when I take 3.5 hour one-way all-highway trips through speed-trap riddled New Hampshire and Vermont, I still only get 23 mpg. Maybe if I drove my car like it was a Honda Insight I could approach 27-28mpg. If I wanted to do that, I certainly would not have spent the extra money to get a WRX over a TS or RS Impreza. If I had a WRX STi, I'm pretty sure my fuel mileage would be a bit worse than I get now. I don't even drive that fast top speed wise most of the time. But I do enjoy accelerating hard up to that speed, and holding it as I go up long steep grades. In my experience, not many speed traps are on uphill grades of a highway. That's where, If I'm in the mood, I go the fastest. I'm guessing the original poster also will get 40,000 or more miles out of his tires. I don't think driving that way is in any way wrong. Just that he probably has the wrong car for his driving style.
- Byron