Mabuchi motor variation?

Evening all, has anyone noticed the extreme variaton in performance among the Mabuci motors that Scalextric and Fly are using lately? I have just been handed a most disappointing Scalextric Camaro. It was supposed to run against their Mustang. The chassis are the same, sidewinder layout. Length and track are the same. The Mustang runs a 4.2 second lap (best on 55.3 feet of track) The Camaro barely runs 5.3 seconds. Two weeks ago I bought two Fly 917 porsches, one runs 4.8 seconds, the other 4.4 seconds. they are tuned identically for competition with each other. .4 seconds is a very large gap on the track. All these cars have their stock Mabuchi motors. The faster motors have been switched among the cars and the variaton lies with the motors. I'm considering always buying the Slot It motor, the way I always buy better tires and magnets when I buy a new car. (So I can spend more money to field a car.) I'll stop whining now. Anyone else?