an electric motor, AC or DC, has only mechanical limitations i.e.-bearings failing, stator or rotor delaminating/desintegrating, overheating/demagnetizing. the only limiting factor is external the motor its self, the esc, the battery, a breaker/fuse (if so equipped) etc. you should be able to see exponential mechanical work (RPM) when x energy is applied, barring any failsafes, rpm will climb until the weakest link gives up. an electric motor is only the sum of its parts, two motors with identical guts will perform the same. thats not to say that some manufacturers puff their claims and some (higher end) manufacturers will understate stats (re: 70's american muscle car manufacturers are a great example), and sometimes the dreaded "monday quality" parts are a reality, where Bob is still hungover from his weekend and maybe lets his quality control slip a bit, but is back to the top of his game come friday. just some food for thought.