Medusa 36-80 or 36-70

[BrianG]

It wouldn't cut runtime in half. Actually, you'll probably gain runtime. It takes X amount of power to launch and run your vehicle the way you want. And power is volts * amps. Whether this power is developed with low V and high A, or high V and low A makes no difference, except low currents are more efficient (less heat).

So, if you find you need 350w average power to run like you want (roughly typical for a truggy), with 3s that's 31.5A, which equates to around 19 minutes of runtime (assuming 5Ah * 2). If you go with 6s at 5Ah, that's 15.76A, which equates to the same 19 minutes of runtime. So, same runtime, but the lower current of the 6s setup will be more efficient, which means less heat. Of course, the motor kv will be different.

A good kv for 6s is somewhere between 1600 and 2000. Just gear up or down to get the desired speed (down if using 2000kv, up if using 1600kv).