Could be wrong so somone please correct me, however, my understanding is speed is Rounds Per Minute and Torque is when you either want 'power' or a quick trigger response
Speed in a gear is how fast a gear will spin. Torque is the turning force or how strong the gear will spin. Basically, the more torque you have, the easier it will be to turn a powerful spring. A standard 18:1 ratio gears will have more torque than a 13:1 ratio gear set because the teeth a gear has, the more torque.
The faster a gear spins, the less torque there is but the RPM will be faster, but not with powerful springs because there isn't enough teeth to cling onto for a 13:1 gear set. The more teeth a gear has, the more torque, you can try it for yourself; open up the gearbox but leave the gears on, now spin the gears freely. If you spin the bevel gear first, the sector will spin very fast but it won't take much to stop it, a light touch will stop it completely but if you spin the sector gear...
Basically, if you want high speed firing, you will need a high speed gear set paired with a high torque motor because the high torque motor will provide the power to pull back the spring more easily. You you have a gear set with more teeth, like 18:1 or more, a high speed motor is ideal because 18:1 have good torque but will not have as much speed, so a high speed gear will speed them up. Don't pair a high speed gear set with a high speed motor.