Thank everyone for your input. Just remember this is another group's debate, not my project of comparison. I have no way of setting up a meaningful comparison for such a debate that I don't own either of the lenses (only anticipating my new 180-600). I agree with Clovis that from a technical view, the new z lens shall outperform 200-500. However, there is just someone who insists his/her images shot by 200-500 with z8,9 are all better in sharpness and IQ than all others' presented images shot by the new 180-600. There are images posted by this fellow to prove his/her point. And I saw no one could directly object, but only turn to other venues (e.g., online posting) of dismissing his/her proof. AW, the thing dragging on and the fellow is still waiting for his/her new 180-600... I hope until then this fellow will self-dismiss his/her point (so I can be more sure of keeping my yet shipping new lens).