As I started all this I thought I would add a bit more. In the end I bought a Tamron 200-500 and have used it quite a bit over the winter and brought it up to Lofoten in Norway for the summer (
http://www.mejhogan.com/gallery2/mai...g2_itemId=301). It is a very good lens, especially if you keep it closed down. However, as it is quite a heavy beast I get the best results using a tripod. I have gotten good results on bright day using a monopod but hand held - not great. So I am thinking of selling it (see for sate items) and changing to this configuration - Sigma 500 f4.5 prime and probably a Nikon 70-300 VR f4.5. This will give me a good long lens for the tripod and a carryable lens with reasonable reach.
Madness or inspiration ;-) ?