The way I like to look at this is great mileage when needed, just cruise and take it easy.
Time to play, does not count, usually.
I built a very fast, highly modified, $30k in mods, Forester XT, it still got 28MPH on the road and playing around a bit...on track, double priced race fuel, 8MPG, ouch! AWD, JDM diffs, JDM or better all other parts and mostly better, 285 slicks, full interior, tuned for fuel mileage over power, modest turbo upgrade so only 275WHP and 280ft lbs, measured at 5,000 elevation on AWD dyno so some losses, 4:44 gears, fast enough I passed a full race STI and the head instructor at MMP came down from the tower to check it out, when he saw the car looked stock, etc, he was blown away by my lap times.
I would drive to the track with as low fuel as possible, half tank of race fuel added, run a session, add a few gallons, run another one, add a few gallons, etc....140mile round trip, 80 minutes on track, $275 for fuel.......for the day, more than most of the track fees.
I am very curious what my ST with an upgraded stock turbo, all the bolt ons, highly dialed in suspension, BBKS front and rear and on 225 slicks at around 2550 lbs will do for lap times and fuel consumption on track, pump gas only.