RE: Monsoon vs. Earthquake.
I also agree with Nitrosports. The Eathquake will be faster if that is what your looking for. My Monsoon runs in the mid 30 mph range. Really 34 - 37 mph is realistically what you should expect from it. Torque is what it does best. It won't smoke the tires on the pavement "only in large part due to the massive tires on it", but you will hear them spin as they look for traction. Even in tall thick grass all four wheels spin hard off the line. The Monsoon would greatly benefit from a bigger clutch bell or smaller spur, if you could just get a bit more top end and reduce some of the torque it would be perfect in my opinion. Unfortunately your stuck with what it comes with, I have not found any optional replacements.
Another thing to consider is if you get the Earthquake, you will be able to use many of the Caldera parts on it. This will certainly help your wallet when trying to keep a back up inventory of spare parts. The Earthquake's power to weight ratio is much better mostly due in fact to the chassis difference. The Monsoon is a beast, it weighs a ton, but works great do to the larger engine. Also, I feel the Monsoon is most suited for the track, this is not to say that you can't run it anywhere you want and still have fun with it, but it handles really well, is almost impossible to roll over and is very nose heavy. It flies great over track jumps where there is a down ramp, this way you don't have to constantly correct in the air to get the rear down. When jumping in the yard on small jumps, this can be a problem. If you don't have enough speed and air time to get the nose up in flight, you'll be nose diving every time.
The Monsoon is a heavier built model, looking under the lids of both sitting side by side there is almost no comparison. The difference between the lightweight series and pro series are very obvious. The pro series comes with a steel spur gear, front cvd's, massive control arms, 17mm aluminum hubs, and very impressive shocks considering the price range. None of this is found on the lightweight series. I think considering the price difference, you get far more vehicle for the money if you purchase a Monsoon compared to the Earthquake. But considering what you want it for, and the fact that you already have a Caldera, if it were me, I would buy the Earthquake.