I agree the 400/5.6 is a classic birding lens, but the OP mentioned 200 or 300, she also sound like she plans to work handheld/monopod more than tripod so the IS on the 300 + 1.4X might be a better solution.
If she were planning to work via tripod and when the light was good perhaps monopod the 400/5.6 is probably a better solution.
I still want the 300.

