This was all done with large deflection turned on (with it off I get warnings that suggest I should use it). I have just done the same simulation without it and with a frictionless support applied to the large faces of the disc and the outer face and instead of the disc twisting and deforming it basically just expands outwards, from its original approx. 200mm diameter to around 10m in diameter, there's no rotation like there is on the lower velocity simulations either. I'm not sure what to make of this but thought I would add it as a note in case it helps anyone to help me.
I have also just ran with large deflection off but without the frictionless support and once again the blade twists and deforms.