Anyone complaining about fuel burn rate being too high should climb to historical altitudes.
After someone on the forums helped me out, I can climb a spit XIV to near 30,000 feet or higher and still have 30 minutes of fuel at max throttle.
With the XIV, once you are at high speed and level, you can decrease with the minus sign and still maintain 400mph with near 40 minutes worth of fuel.
Some planes don't respond to pulling them back with the minus sign, though.