A "switched" battery pack could work well for something like drag racing.
For typical driving, it's not really ideal. Just go with higher voltage for better top speed. With the increased voltage, you also need fewer amps for the same work, so your batteries will tend to live longer.
Let the PWM controller do all the hard work for you.
My
"Turbo-circuit" was basically a switched battery pack. It worked frighteningly well, but I will be much happier with a higher voltage controller!