It might confuse you more than help you but have a play with the numbers in the
RC Car/Truck Power & Setup Calculator (rough estimator) to see how the variables interact by changing them.
For 1/18 scale trucks that weight ~600g I prefer 3s on 11.1v ~5000Kv motors geared for 35mph, for streeet bashing it delivers a good compromise for action, run time, cool running, component life span, cost and usable top speed.
You might see a few 2s setups running crazy high Kv motors, I think that's because they might be chasing tall top speeds when operating with lower voltages the high Kv helps to avoid running out of max pinion size head room. Also the higher power 2s setups waste a lot of energy as heat, drawing too many Amps and give 2s packs a harder shorter life.