A dime of commercially priced electricity is around a kWh depending on where you are. That'll take a car a lot further than you think, and the more aggressively you drive the more electricity gets used. The most efficient way to drive is the flattest, most leisurely route.

The only way aggressive driving becomes profitable is when you've exhausted your supply of cars. Even then, it's not clear to me that you'd increase profit in that time by driving faster, since one car over the course of a day might squeeze in one or two extra rides at most. Just having more cars that sit idle until needed would accomplish the same thing with no extra risk.

In fact, the biggest area for optimization is getting the car to the next rider from the end of a previous ride. But that's not about being fast, that's about positioning idle cars in the right places to minimize distance to potential riders. If pickup distance becomes a hard bottleneck, it's again about capacity, not speed. Most of the between-trip driving is not on highways and back roads, it's through dense areas with lots of stop signs and traffic lights, so increasing speed isn't even really feasible.