I have Mambas too. But I have 1 Novak ss sport 5800 which I think is same as yours ? but much older. I use it in my Dark Impact buggy and it is real smooth and has plenty of power with 6 nickel cells.
The SS5800 has a little more top end than the XBR 8.5 so it's faster than what he has, which is the 13.5 equivalent to the SS4300.