What should I do?

[What's_nitro?]

Well, you have two complete vehicles there. Unless you plan on buying another to put some stuff in, perhaps you should think about selling off some of it. The 9920 can't run the 600xl due to the ridiculously small RPM limit on the 9920. Your two 3s packs would be a good combo for the 600xl IF you had another MMM, or could stand to swap it from car to car.