If you can find a BJ4, I'd have to say they are very solid indeed - less plastic parts than the B44 (I know one chap who's gone through 6 B44 front bulkheads), though plastic isn't a bad thing in certain places. I bought a BJ4 that was a wreck and barely touched it through my first year of racing - broke a few things, but nothing I wouldn't have expected from the hits that caused them! It's going better now than I got it - finally getting on top of the maintenance!

This one is a good offer which I'd have taken myself but for the fact I'd end up with too many BJ4s!

Otherwise, a plastic shaft-driven tub chassis sounds best - BMAX4, Cyber 10B, DB01R (the hopped up version of the Durga).