Thanks all!
Leon - I'm with you on the diffraction spikes. I don't like them in images of galaxies and nebulae, but think they look OK when imaging stellar clusters. It's an interesting conundrum.
Dave882 - The stars at the centre of the cluster are rather blue/purple. This is how they came out of the camera, and I was trying to emulate one of the images on Telescopius that showed them in a very similar way. Not to everyone's taste, I do admit.
Cheers,
V.