I finally got my brain around how this works, so thought I'd pass it on. As we all know already, torque is the measure of force a motor produces at any given instant, while horsepower is the rate at which a motor can do work. In real life, they are directly related through rpm:

HP = T x rpm / 5252

To understand what that means, lets look at two motors that both make 130 lb/ft of torque, except that motor A has peak torque at 3500 rpm and motor B has peak torque at 5000 rpm... we can calculate HP at the torque peaks:

Motor A = 87 HP
Motor B = 124 HP

What accelerates a car, however, is neither torque nor HP -- it's thrust at the drive wheels. The motor that has its torque peak at higher rpm can stay in lower gears longer, which means that the torque is applied with greater mechanical advantage than the lower rpm motor = more thrust = quicker acceleration.

Obviously, it's desireable for a motor to maintain a torque level close to peak over the rpm range needed to get all the way through each gear, and that's where the one with the most area under the torque curve determines which is quicker. BUT, for two motors with the same area under the curve, the one with the curve occuring at the higher rpm is quicker.

Now let's all go out and build great motors... (j/k)

8^)