motor for emaxx on 3s ??

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hey ,

i have an emaxx 16.8 with the flm chassis ......, and im looking for a new brushless motor for it , im looking for speeds of 37-40+mph on 3s lipo without overheating , should i get the 9l , 6xl , or 7xl , the gearing i have r 20t , 24t pinion and 62 , 65 , 68 spur ?or suggest any other motors but the max im willing to pay is 60 - 75$ for a motor.

thanks