The f4 is sharp but the 2.8 is sharper and sharp wide open which is really were it counts. Both have 4 stop IS which depending on your view is either a good thing or not needed. Personally I would rather have it than not.
If you can live with the price difference and see the extra stop as beneficial then buy the 2.8
He said F4L or F2.8L mk2 so they don't both have IS
Hi al, there has been a lot people saying the f4 is sharper and some say no the 2.8. Is there anyone that has both, as I am considering on the idea of upgrading from my ef70-200 f4 is usm which I have used about 5 times so far.
Compare the weights before deciding.
This is the best advice. Forget the sharpness, aperture or IS, which isn't going to be that noticeable for most shots, but the extra weight will be for every shot.
You'd have to be pixel-peeping to see any difference in sharpness, and there's probably as much process variation between copies of the same lens than between different models. I had the 2.8 (admittedly the mk I, not mk II) and actually swapped it for the f4 due to the weight. Both are great lenses but for me (and I'm an amateur not a pro) the 2.8 was too heavy to lug around.
. f/4 is very small and doesn't weigh much more than a smartphone;