So normally I wouldn't consider getting one of the giant super teles, as the cost is too high, and I wouldn't use it all that much. But looking at a bunch of used equipment retailers on the web, I've noticed that I could actually afford one if I didn't want a new version with all the latest bells and whistles (although I'm still unlikely to get one, I'm mostly curious). The costs seem to be
700-1000 ED IF version (no autofocus)
1000-1500 AF/AFn version (screwdrive)
1500-2500 AFI version (built in autofocus before AFS was invented)
2500-3500 AFS version (non VR)
And we all know how much the VR versions cost. I wouldn't consider 3rd party models (even new).
So I'm wondering if any of you guys have actually used these lenses (not just read the reviews, since I've already read most of those). How good are the optics of the old lenses? And how does the autofocus speed (on say something like a D90) compare to some of the modern lenses (let's say 70-300VR for reference)? And is it really worth it to get the VR? If I got one, it would be mainly used for shooting birds in flight with a teleconverter (and obviously with a Wimberly or something similar).