So the rear plate is the new one, the front plate is the existing clutch.
By my scientific measure (how far up the mechanical pencil point) the clutch has worn about 1mm on each side, so I'll keep the existing in for a bit longer (done about 70,00 at my guess).
I now have the question of why did my clutch slip... I noticed when cracking open the gearbox a bit of oil & moisture ran out from the bell housing, and the housing was quite oily inside. So that could explain the slip. With no obvious sign of leak from the crankshaft it appears that the oil must have come through the throw out fork hole (the boot keeps popping out).
Now the mission to lift it back in. Suprisingly the gearbox is not as heavy as I remember.