William, your answer is very comprehensive, and my decision is almost made.
It´ll be a 105 mm. Sigma or Nikon. And i ponder about the possibilities of using the teleconverter, have to check compatibility with both brands.
Robert, the Tamron was given to my by one of my sons, last winter.
I started out shooting cormorants at night in freezing cold, with handheld torch light,and the D80 body. ( I had some shots from this in my portfolio, but deleted as I want reprocess them)
Experiences from this started my equipment escapades:)
Fabs, I know from my Sigma 70-200, that the teleconverter doesn´t fit, but i could be different with the 150 and 180 mm. I will check:)
Fabs,William and Robert, Thanks for your input here and have a nice weekend!