It all depends what motor you are using. If you run modified with low turns motors then yes, you want a low IR for the max punch and speed. With high turns motors the current draw is much lower and so the voltage loss over the internal resistance is also much lower. The main electric class I drive is 1/10 scale F1, my packs in a good condition have 3 mOhm per cell and my bad packs have cells of about 8 mOhm and it is hard to notice the difference on the used 21.5T motor.