I did a fair amount of research on this when buying a Nikon 600/4 (I bought an AF-S 1 in the end)
Yep, the AF-I doesn't use a screw-drive mechanism... but it is very slow to AF compared to AF-S. Noise when using AF is louder but not too bad, I've heard worse. The 400/2.8 AF-I is the real 'dog' to avoid by all accounts. Besides, birds are more likely to be scared off by the sudden clatter of the camera rather than the AF noise... and at times, a bit of noise to catch the subjects attention can be a good thing as far as photogenic poses go, just as long as they are not spooked into flight.
Although some optical redesign was done for the newer AF-S lenses, there's not much difference in the actual quality of image.
I'd watch out for oily/rough aperture blades on something this old. Given that it's about to be an extra generation old, I wouldn't want to pay more than £2000 for a 500/4 AF-I.
You may have seen this already but there's a review of this lens on BF
http://www.birdforum.net/reviews/sho...duct/69/cat/14
Cheers,
Andy