Will this setup work?

[RC-Monster Mike]

Gearing for speed is kind of the opposite of how your truck is set up and where you run (tall tires on a heavy truck in a harsh environment). For everyday running in that environment, I would gear around 15 or 16 pinion on your 51 spur. This will put you in the high 30mph to low 40 mph range. For speed runs (assuming your speed runs will not take place in the quicksand!), you can gear a bit higher and get into the 50s fairly easily.