That's a lot of power in something so light! Tires are available, personally I would go soft, but they will chew up fairly quick for that sort of power on asphalt. That said, I don't use mine to bash so I am happy to use quicker wearing tires.
Grooved, I don't know. Someone else may, personally I would stick to slicks (unless you want to replicate a rainy lap!!) but as much as anything that is my desire to look scale on my vehicles.
My gut says to go to a lower motor again, 21.5 / 25.5 area. See how it goes, you may just be overpowering the chassis.