The push me pull me is a dust hog. Birding is field photography ergo I find the 400 prime a better selection.
The "dust hog" or "dust pump" nonsense is just that - a silly internet myth propagated by people who have never actually used the lens.
If the OP is planning to buy a newer lens, he shouldn't worry about getting a "soft copy" - the early problems with quality control were cleaned up about 10 or 12 years ago (this lens has been in production since 1998).
Why would people lie? I heard that the 100-400mm and the 17-55 were dust collectors. I don't have any experience with them, but I do stay away from them because of the rumors. Of course I have spent a ton of cash on other lenses... so it's not like I'm missing out.
So you might have missed out on using great lenses because of those rumors. The rumors did their job!
I had the 17-55 for about five years, and it gathered a few specks of dust that I could see, but nothing that would qualify as a "dust pump." None of the lenses are air tight, so dust can get in any lens. If you have questions about a particular lens, it's more accurate to get informed opinions from those that have used the item. The internet has many opinions and a lot of them are wrong or not representative of the collective user base.
+10 Additonally, we have no idea if these people reporting these issues have a clue as how to properly switch a lens out with another one or even just to take a lens off to put the gear up.
My dad taught me almost 30 years ago with my AE1 and F-1 that the most crucial thing I did with his cameras was putting on and/or taking off lenses. He drilled it into me and I've always taken great care and maximized my speed and efficiency at switching lenses in the field. I guard the openings like they are my last dollar! I check everything twice before I start a change and then do it very safely and very quickly. I've never had dust issues.. just haven't.
My uncle on the other hand, very good photographer yet all his images are filled with dust particles, with lenses not "known" for being dust pumps!