It will probably be okay if you don't make long runs with the settings turned way down like BrianG suggested. A MMM would be a safer bet, but not as versatile in case it doesn't get used. Those batteries should get the job done, a newer (not worn out) set would be helpful. You may think about setting a 3.2 or even 3.3 volt per cell cut-off. Also be sure to keep an eye on esc temps. I wouldn't be surprised to see the fan kick on after heavy bashing for long durations; but if you allow some airflow under the body, it shouldn't be a problem.
It would be nice to have a data logger or watt meter to measure the current draw under heavy acceleration. There are going to be some pretty big amp surges getting that thing moving; I would suggest avoiding any tall grass and mud. Like others suggested, I would recommend that you drop the pinion down a bit. If everything runs cool on the lower gearing and you want more speed, you can always move back up. It's easier to put on a pinion than it is put the magic smoke back in the controller.
We really only intended the Max Pro to be used with buggies; but I think
the conservative setup and having the settings turned down will work just fine. Can't wait to see some pictures or even some video of it in action. Good luck!
Thomas Porfert
Castle Tech Support