Thanks everyone.
I nearly processed this image with the delete key.
The heavens had really opened up when I took this hand held shot, rain, hale, sleet, snow, wind, everything that nature could throw at it and at me, so even though the image is as sharp as it can be, there is so much atmospheric blurring going on, it has sort of naturally softened some of the edges of the detail.
I have had the shot languishing on my PC for well over two years now and never been inclined to work on it, as I thought it was a bit too dull to produce anything worthwhile, but then one of my photography visitors noticed it when I was scrolling through some files in bridge and absolutely raved about it. So I thought I would see what could be done with it - if anything. But the light in the shot was so low, that even straight out of the RAW, the file had some posterisation problems in the darkest areas of the sky, but then I remembered a trick that Jeff Schewe once mentioned about how he used film grain to alleviate the effects of posterisation and noise with his old Canon 10D (yes Jeff, you can come over as a grumpy old so and so at times, but I have to take my hat off to you and admit that you do know your stuff). So that's the route I took and by applying the minimal amount of film grain I could get away, I was able to completely smooth out the posterisation and it worked.
Printing, not so sure about that, because even though the 16 bit tiff now looks really good backlit on my screen, from experience I know that trying to get an image with so little light in it successfully out onto paper, might be very difficult indeed, but what the heck, I might as well give it a try.
Thanks again everyone, you have given me much food for thought.
Dave