Hi Mate,
Just replying to your comments about my Nankeen Kestrel with M400 lens...
The Kestel shots were from a long way away and cropped a lot, they were also handheld. In my experience these factors definately make the resultant shot less sharp
I like the lens, but I do find on digital it's hard to get it all just right. I do think it's capable of great sharp images, but at times these can be hard to get. I usually use the lens on a monopod, and with enough practice can get photos that I feel are sharp enough. However I also just got my first good tripod, and with some quick tests the results seemed to be much sharper straight away. Unfortunately I don't have any good examples that I can show you at the moment. I suggest you have a look at 8540tomg's bird shots, he has had some really good (sharp) results, that you should be able to find fairly easily on this forum.
cheers