Why would would I ditch the 2.8 II for the f/4 version? I've been toying with this switch for some time now. Finally jumped.
IMO the the f/4L version is superior, regardless of cost!
Yes the f/2.8 version has slightly better IQ and is 2.8. I believe the IQ is inconsequential. The vast majority of people will never notice a difference, thus leaving the sole advantage being one stop of light.
So in my mind it boils down to:
one stop of light vs. a smaller, lighter, image stabilized (4 stops of light), and a dedicated macro function.
Is my logic flawed? Why? Help me please. What should I do with the extra $800?