Cool. Stay away from maxamps, gens ace are good batteries, a lot of people also like the cheap batteries from hobbyking.com.
To figure out a pinion size, you usually shoot for a 40-45mph top speed on monster trucks.
In order to figure out a top speed we need to know the variables mentioned above- tire size, motor kv, voltage, diff ratio.
In my opinion a novak system is a little small for a big monster pirate. My recommendation would be a castle creations mamba monster speed control and 2200kv motor on 6s.
Top speeds can be figured out here>
http://www.scriptasylum.com/rc_speed/top_speed.html