The Izumi Standard Track chain came today and fitting it reduced the noise from the 1Z1 chain. The profile of it seems beefier, thicker plates than 1Z1 and excellent sticky lube was already applied. There was still friction though. Scilly, you were right about this:
The vibration is coming from the "chain suck": as the chain pings off the teeth it vibrates.
Looking close up and moving the pedals slowly I can see the square teeth of the Planet X cog is hanging on to the chain, like it is catching. Then it is dropping off, this (I think) is causing the sound at higher revolutions. I had a play around with shifting chain line around; sitting the wheel on top of the dropouts with the bike upside down. I got the chain line damn-near perfect. The chainring and cog teeth were sat bang in the centre of the chain plates. and still sound, and the chain suck. Conclusion is that it has to be the sprocket, the carbon frame is acting as a loudspeaker to whatever vertical friction is happening there. So now i am looking at getting a sprocket with a more pointy profile to the teeth and a shinier finish. My chainring has pointy teeth and no such chain suck is happening there, so I'm hoping that will solve the problem.