e57, the best comparison I could suggest is to see how many holes each can make on a charge, and in how much time. For example, using a 1" auger and drilling through a 4x4, I'd be willing to bet that the 24v will drill almost twice as many holes, and in about the same time.
Plus, for the 18v to have almost the same torque, the chuck RPM at max torque would have to be quite a bit lower. This is simple physics. A small 4-cylinder engine can produce gobs of rear-wheel torque if you gear it low enough.
