MR vs. FR layout. More weight on the rear axle for the MR cars, thus more grip when launching, which equals a better launch. Keep in mind that the launch stat in Forza doesn't depict the usual 0 - 60 acceleration, just how fast the car will get away from the line.
You'd have to take the launch stat and the acceleration stat into account to reflect a car's 0 - 60. Haven't checked these, though. I generally wwouldn't read too much into Forza's stats aside from the HP figures, weight, weight distribution etc. They're generally not that representative.
