I normally get 320 miles per tank (commuting and driving hard when the road conditions allow), but I have managed 427 miles out of a tank (driving carefully).

My fuel gauge give me more miles for the first half of the tank than the second half (i.e. the needle drops quickly once in the red).

I wouldn't worry about economy with the cost of gas in the US; enjoy the performance before our government(s) make it impossible to go fast.