Thank you so much for this subject I think I will do this weekend the same pic to flamingo with my older Sigma 70-200 F4-5.6 and the last 70-200 F2.8 Apo EX DG macro. and check the diference. I´m sure will be some and you can comment better..you know many more about that.. Than you so uch for this thread is very useful to me. 
Thank you very much Tom, Danny, Onslow and all the people write here..