I haven't fielded any questions regarding these little buggers yet. The Castle system you have is probably one of the best available. I am working on stocking another system as well, which should be comparable to the castle systems.
the rc18 or the mamba 8000 bl motor? - I would have to say yep - I run mine with the mamba 8000 and on its second highest setting ( 2 out of 4 ) - it does double backflips. And the diffs have held up fairly well - a little barking now and then but they are still intact. The little bugger is so much fun and fast as all get out. I also run hpi rally tires and rims on mine....
Cool -
My MiniT I will be going brushless soon. I put the Mamba 8000 in my Schumacher Mini-Monster. That is way to much power for a 1/20 scale truck. After I get some video, I will put a Graupner 300 in it instead. ;)