I have an HPI Wheely King, and I love it. I stretched the wheelbase 2" with custom-made links, using Revo rod ends, and Traxxas E-maxx shafts. Then I added a Multiplex 600 motor, and locked the rear diff. It crawls great, is about twice as fast as stock. (ditch the crappy battery that's included and get yourself a good NiMh batt.) and as for mud, well... I'll let the pics speak for themselves.





Btw, here's the stock, out-of the-box crawling ability:



I have about an extra $65 in it, and I LOVE IT! I've beaten the SNOT out of this thing, including lots of high-speed jumping (several times off my porch, nose-first landing) and so far I've broken 1 lower link mount, the front upper link mount is pretty messed up, and I bent one axle shaft. The weak points are as follows: Upper link mount, upper y-link, rear steer lock-out, servo-saver, ESC. that's about it.

Plus the WK is RTR, the AX10 needs assembly, plus electrics and radio to go. (there's another $150 easy.) The WK you can up-grade as you go.