I have a xxx-4. I think if you want it to be a tank, you would need
carbon graphite shock towers, aluminum pivot support set, and maybe an extra belt if you want. So far, my front shocktower and front pivot support are the parts I broke. I also advise you to use a mod motor or even a brushless(novak ss5800 would do).
Here's a link for aftermarket graphite shocktowers:
http://www.artshobby.com/store/about...d=207&compid=1
http://www.artshobby.com/store/about...d=208&compid=1
I hope this would help you if you choose the xxx-4.Other 4wd choices would be the Jconcepts BJ4, Kyosho Lazer ZX-5, Losi xx-4 WE, and others like predator X-10 or (x-factory) X-5. I haven't used a 2wd buggy but many say it's good and many use it too. It's your choice.
