Overall - It does REALLY well!!! I need to adjust the suspension a little. It's too stiff. There are tons of adjustment points on the chassis/axles so this will be easy. I also need to get 4WS hooked up badly. The stock tires grip well and are soft and work good. Kong tires will fit right on these wheels also.
Durability - Everything held up fine! I got the wheels jammed up several times where they couldn't spin and applying full throttle didn't do anything to the gears. I also jammed it from full speed reverse to full speed forward on pavement and there was no problems. It just did a little wheelie and took off. The gears were the only thing that I had a concern about becuase they were unproven AFAIK and they held up great. I'm very impressed!
UPDATE 09/29/06
More crawling pics
New chassis shots
Pics of it crawling: