Score = ( square(max cruise speed in knots) * max range with 45-minute reserve in nm * payload with full fuel in lb) /(dirty stall speed in knots * fuel in gallons)
This score says that it is VERY good to have an airplane that can go fast, and can go far, and can carry a lot of people, and can go slow enough to land safely at many airports, and is not too expensive to fill up with gas once you DO land.
In other words, this score is one possible indication of how good an airplane is.
(note: we SQUARE the speed because the DRAG on an airplane goes up with the SQUARE of the increase in speed, so it takes FOUR times the thrust, or one QUARTER the drag, to go TWICE the speed. Also, we want our airplanes to GO FAST. I mean, X-Plane.com is not about tugboats, right?)