So I've noticed that if I connect two EV3 motors to one another (with gears), I still get exactly the same maximum speed as if I had a single motor.
So, my question: how can I get twice the power/speed out of two motors?
Update: here's an interesting observation: if I get both motors to spin as unregulated, I get a much higher speed than if I get them to spin in a pair (e.g., B+C move tank).
Update 2: ended up building a differential as per accepted answer: