RE: More power=new bandit :)
If you are running a VXL model why not just get a 3S LiPo and be done with it. For the price you're going to pay for a max amp battery you can have a 3S Lipo, a Charger and a balancer and still have change left over.
Don't be surprised if the car isn't much faster on 10.8V NiMh. That pack is going to be heavy..