In my opinion if you run stock brushed run the QC2 or the GTX. I ran both LRP Sphere and Novak GTB brushless and for stock racing they didn't perform.
LRP Sphere is the easiest to set up and use on brushed, but does not come with fan or run capacitor which is needed for hotter motors , and the programming is limited.
Now I'm running the Novak GTB, it comes with the optional fan and a run capacitor. It has all the optional custom programming you will ever need. No computer needed.
You can easily run the 13.5 motor all the way up to the 3.5 motor which is about 8 different motors to choose from in speed. They have great tech support and warranty support. Tried and true. I'm sold on the Novak brushless system, been running it just at a year and have had no trouble. Soon I'll have all there race motors. And you can get there sintered rotor in every motor they make now. You should check there web.