I also forgot to mention that for the 4x4, you also have the option of a center differential instead of the slipper clutch. The slipper clutch sends 50% power to the front and 50% to the rear, while the center diff sends more power to the axle with less resistance. For example, the car's weight...
The Ultimate is pretty durable for the most part and handles pretty well out of the box. Give it a run stock, and upgrade anything that breaks.
The most common parts that break on the Slash 4x4 include the plastic driveshafts and... honestly, that's really about it on the Ultimate other than...