[digirebelva]

I have also heard that the F/4 is the sharper of the 2, I guess it comes down to how much shooting indoors in low light you are planning to do..Outside of that, I am not sure you are going to see that much of a difference in IQ to use that alone in making your decision. I have the F/4 non-is version and when its on its sharp no doubt. I'll let the photogs with the F/2.8 chime in with their experience