Sigma 50-500 non-DG version?
I have the bigma non dc version. I use it for birding. I also uses a cheap 1.4 TC with the setup. I origionally used a 10D but upgraded to a 20D and a signimonster.
The result I got were very excellent and if you use photoshop to post process you should get very acceptable results.
I now use my bigma for general purpose shots like plants and doings like people at parties etc.