[Batfish]

If you're racing on a track, you'll never get to the top end of the 4200 :)
I had an xl4200 and MGM12012 in my XXX-T MF. With 6 nimh cells the only time I ever got it to full speed was in about 100 ft of parking lot space. 2s lipo will be about the same top speed with much better accelleration. The xl4200 will be all I ever need for racing. If I want to break the sound barrier I'll try the 5000 or 5300 :)