Why do you expect it to be better? I have the 3.5, and it's a superb lens - the biggest issue is slightly dark corners wide open, which disappear by 5.6 or so.
Originally Posted by nwilkins
The main reasons to use the f:2 version are (of course) the maximum aperture and it's attendant shallow dof, and the close range correction. High speed films have improved greatly, so fast lenses aren't as neccesary as they once were. The other aspects may be important to you though.
As a sort of parallel, I once had the 35/2.8 and the 35/2, both pre-ai. I kept the f:2 because it had more even illumination.