Danny,
I would personally have looked at a brushless setup since the motors are sealed and beach running would have worked much better then.
A 9 turn is pretty hot motor, can the chassis handle it? If so, I would go with a checkpoint or trinity shock motor. something that doesn't gum up in the dust (V2s can gum up in the brush hoods) and gets long runtime between motor comm cuts.
Ultimately, a brushless setup probably would be best.
Assuming the cost of the GTX and a checkpoint motor, not too much price difference than just getting a Mamba max system. And you will need a lathe for the checkpoint still.