70-200 f2.8 / f4 sharpness and IQ

If this helps, I would be comfortable croping to nearly 100% with the 70-200/2.8. Any softness I've encountered is user error, or simply subject movement out of the focus zone before I can catch up (sports are killer =D). It's very sharp at 2.8, and a f/4 it's unreal.

I have the 2.8Lis version and had the f4 and to be honest you would be hard pressed to tell them apart as far as IQ goes,both very good with the 1.4 T-con,but for me Ile take 2.8 over f4 any day.

I have both; and they both have their uses. If it's daylight out and I'm going light; I'll bring the F4. If I KNOW it's going to be questionable; I bring the 2.8

Personally I just couldn't spend the extra for the IS version of the 2.8
If I were a Paid Photog for weddings or other gigs; I probably would, but for me the 2.8 has done what I've asked of it so far..