As luck will have it, I spotted a guy running practice laps on Friday with a Kyosho, he was a novice level driver and was really putting the car through a lot of abuse on the track, very rarely was he able to make a single lap without having to be marshaled. All I have to say is that I was extremely impressed with the durability over the 4 hour period of abuse I saw him put that car through!
I asked him what he thought of the car and he explained the only part he ever seems to break are the cast aluminum spindles at the kingpin hole. He says he breaks at least one of these every single time he come to the track to practice, but I have to imagine that an average sportsman level driver might rarely break that part.
Based on what I saw, I might say that Kyosho is on par with durability with HB.
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Here's a video clip following Brandon Rose around the current layout which is probably one of the more difficult layouts I've seen at Thornhill:
https://www.flickr.com/gp/bill_delong/x70B487g53