Border added and processed thru Noise Ninja...
Thanks everyone for the encouraging comments!
Seaain, Thanks for the suggestion about the noise reduction. I had actually tried it on the full-rez version and the results were not satisfactory, but it worked ok on the downsized version.
Josh, I'm almost embarrassed to say "yes, I really did shoot this at f19". I shot several frames like this with the ISO up before realizing what the aperture was (I was a bit bleary that morning). I actually opened up the lens to f8 and decreased the ISO to 100, but by that time the mood and clouds had changed significantly. The lower ISO shots are much less interesting cloud-wise and without the "grain" they look very flat.