as marc said, forget about crop factor, it is a misleading concept. as you are only shooting aps-c digital slr's, focal length is focal length, you know what 200mm means to you, that's all you need. focal length does not change across formats, a lens of a given focal length will behave as you expect that focal length to on your camera. if you must have a way to compare across formats, take the time to think in terms of degrees (field of view) instead, it will save you a lot of trouble on the long run.
many people who know what they are talking about (note: _unlike_ me) point out that you need to learn how to get closer before investing in longer glass, in the case of birdning/wildlife, you need patience, passion for your subjects, and knowledge about them and their habbits. or so "they" say. ofcourse that's not to say there is no need for 400mm or longer, it's jsut something to keep in mind.
i own and played with a pentacon 300/4, manual focus, excellent optics, excellent build, f%$^ heavy (i do mean it, i managed to handhold it for about 10 shots or so, before i gave in to the pain in my left hand), i estimate about 2.5kg. it tends to be cheap to buy. oh, it is also big, not just heavy (light surface to air missile launcher - big), as it was designed for a 6x6 format camera. it is great for nailing precise focus, but terrible for tracking fast moving subjects for the same reason (long focus throw, heavy dampening), so prefocusing is your best bet. i still love it
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hope this helps, good luck with your search, let us know what you shoose and how it suiths you.
edit: one related "trick" is to try and go for the bigger birds at first, for which a "mere" 300mm, or even 200mm might do the trick. this may not be acceptable to you though.