Depending on the speedo, you most likely want to run the -4 dot insert (take motor timing away), especially if you run timing advance/boost/turbo in the ESC. The X-12s are very tolerant of heat (they seem to like to run close to 200 degrees). Ask some racers at your local track what gearing they are running to get a ballpark rollout/FDR/gearing. Then check your temps, and adjust accordingly.
What class are you running and what motor? 1/12 scale, TC? 17.5? 1s or 2s LiPo? What ESC?
*** The Gate - Celebrating 7 years at the same location ***
The difference between genius and stupidity is that genius has its limits. - Albert Einstein
Understeer is when you hit the wall with the front of the car and oversteer is when you hit the wall with the rear of the car