Just to have some input. For those who haven't been involved with karting as much as Darren has, 219 is used almost exclusively on high powered racing karts. It's strong, compact and has a huge variety of axle sprockets available and very cheaply. (under £6 usually) and in one tooth increments. I used it because of those factors on Kim, and it was only because the axle moved that I had issues. I would not hesitate to use it again IF I could get the sprocket for the torque converter. If/when I make progress on another CK it will use 35 chain. Proven to be strong enough, lots of axle sprockets (cheaply) and not as bulky to deal with as the 40 series chains, some of which will give clearance issues.
I have just been speaking with Gemini, the supplier that made those sprockets has changed ownership and they say much more difficult to deal with than the previous regime. I am doing some overseas questioning.