Canon 70-200 f2.8 II vs. f4.0 IS

[psnl1]

Looking for some clarification...

With everything else being equal, would you expect to see a discernible difference in a picture take with f-stop 4.0; shutter 1/1000 between the Canon 70-200 f4 and the Canon 70-200 f2.8 (shot at f4.0)?

If you already owned the f4 IS, is it worth the nearly $1k extra to get the f2.8 IS version?

Thanks for your comments!   

[neuroanatomist]

On test charts, the 70-200/2.8L IS II will have a very slight advantage in the situation you describe. In real-world shooting, likely no discernible difference in that scenario.

The real issue isn't IQ, it's if you need that 1/1000 s and can only get to 1/500 s as high as you're willing to push the ISO, or need shallower DoF for portraits.

The difference between f/2.8 II and f/4?  $1000.  The difference between needing an extra stop and not having it?  Priceless.   

[PackLight]

Looking for some clarification...

With everything else being equal, would you expect to see a discernible difference in a picture take with f-stop 4.0; shutter 1/1000 between the Canon 70-200 f4 and the Canon 70-200 f2.8 (shot at f4.0)?

If you already owned the f4 IS, is it worth the nearly $1k extra to get the f2.8 IS version?

Thanks for your comments!   

Yes the f/2.8 is worth it, and at just a bit less than twice the weight of the f/4 it will keep your arm in shape lifting it.

[tron]

at just a bit less than twice the weight of the f/4 it will keep your arm in shape lifting it.

Interesting way to put it