Cliff asked 'had I considered the image in black and white?" I did try it, but didn't even save the image, preferring the colour version. I've redone the monochrome image, adding a bit of contrast, but still prefer the colour photograph.
I think there is more to be done with the black and white image, but I doubt that at any point it will become better than the colour, and if so, why bother. Definitely not always the case.