A monster is a good choice if the track is a little tight and short. For longer or more wide open tracks, the Binary Roar Stock is also a good choice. a 120/34 will get you a 7.51 final drive. How you figure that out is to divide the spur/pinion then multiply by 2.13 (the internal ratio on the 04). I've used HPI, RW, Robinson, and others for spurs, they are all decent.