I've been mulling over this since I bought the 70-200mm f/2.8 IS II this past weekend. Not sure if its buyers remorse or rookie mistake in not realizing the capabilities of my new 5d MK III.
I currently use a 5d MK III and while using my 24-105L f/4 i noticed that I can easily shoot dimly lit indoor scene (church wedding, night indoor events, etc.) just by bumping up the ISO to 8000-10000 and the images look very good still! I have not notice any drastic increases in noise and even so I can get it out using software. Now I have not tried printing these shots yet BUT even in 100% crop the images looks good.
Is there any merit to this line of thinking that f/4 lenses are good enough to use for dimly lit scnese using the 5d MK III? Should i exchange the 70-200mm 2.8 IS II with the 70-200 f/4 IS and save the $900 difference and apply that to a 16-35 MK II or the 35 L? Your opinions/experience would be great on this! thanks in advance!