Hey, I actually had both of these cars. Basically the xx-4 has great rough track handling, which is a Big plus over the xxx-4, but the single belt drive train is so much more efficient, it allows you to lay down the power immediatly!
The cool thing is you can buy a xx-4 and try it to see how it fairs against your local competition. if you feel your missing something or not keeping up, you can buy the x-5 conversion which transforms your xx-4 into an x-5.
Then you will have the rough track handling you desire and all the snap and immediate power so you can lay it down and pull some big power out of the corners.
TeamXray RCAmerica Hudy Xlgraphicspro Paint/ Impulse-Rc Clutch shoes.
Xray XB 808 O.S. Speed Or Ninja JX