To be honest, I have few if any problems with my 200-500. I've gotten some great, tack sharp images with it, and continue to use it as my primary "long" lens. I thought seriously about buying a 500PF but, based on reviews I've read and seen (including Steve's), I didn't think it was significantly superior (if at all) to justify shelling out $3500; I just didn't think it would elevate my imagery. I've compared the sharpness of my images to others captured by friends shooting a 500PF, and I simply can't see any real difference. Overall weight isn't terribly important to me, although a faster AF is always attractive.Steve and others have indicated that the center sharpness of the 200-500nn f/5.6 is very close or even equal to the 500 f/5.6 pf. After saving my pennies for quite a while, I found a used copy of the 500 pf at a price I could manage. I just took it outside and took a few test shots and already I see better sharpness than I was ever able to achieve with my 200-500. This is not to say that the 200-500 wasn't fairly sharp, but the 500 pf is clearly sharper. Maybe this is the typical variation between copies of the 200-500 that people talk about, I don't know, but it's got me wondering.
Also, of course, the 500 pf's AF is snapper, and the lighter weight makes it easier to handle. I think I'll be quite happy with this lens.
Anyway, are there others out there who have seen a significant improvement in center sharpness with the 500pf over the 200-500? Maybe my 200-500 is not quite as sharp as the average 200-500?
So, I'm saving my pennies to buy a 600mm f4 E, because I KNOW that will give me far superior images. In the meanwhile, my 200-500 f5.6 is getting plenty of exercise.