The MX-4 and the MR4BC are the two 4wd buggies, they used to make a conversion for the MR4BC to make it a 4wd truck. I don't know if Yokomo USA supports the cars or not. I hope so, just got an MX4 off of ebay.
Masami did make the A Main at the Losi race (world's warm up) with a Yokomo. It was his own version of the MX-4 (i.e. highly modified). So in the right hands looks like it could be competitive.