Everyone assumes that more torque will allow you to lift a heavier load and that is not true. The amount you can lift is proportional to the power supplied to lift it. You need more power to lift something heavier and less power for something lighter. Power = speed x torque. Speed is proportional to volts and torque is proportional to current or Amps. So Power = volts times amps. So if you have a 12V/5A power supply the power is 60 and a 5V/5A power supply the power is 25.
I have taken and tried to lift a heavy load with a PC power supply and wiper motor and the 5V will lift a bit and then stall out. So I connect it to the 12V.....twice the voltage should lift it right? Not a chance and here is why.
By the image above I have 12V @19A = 228 and 5V @ 55A = 275
Hence less power In = Less power out.
Look at it like a lever arm with a fulcrum The load to lift is constant. The voltage is the fulcrum, closer to the load is higher voltage or speed, the weight applied to the other end is the current or amps. If the fulcrum is closer to the load then the lever arm is longer meaning you need less eight to lift the load. If the fulcrum is closer to the weight the lever arm is shorter, so you need more weight to lift the load.