I am planning on purchasing a new camera body and are anxiously awaiting the new Nikon announcements over the next couple of months. I currently use either a D3x, d300s, or d7000 on my 600VR or 300VR. I consider myself to be an advanced amateur with a lot to learn about bird photography. I am torn as to whether to purchase either a D4 or D800 full frame if the current rumours are correct or to wait for a possible D400 crop camera later in the year. It appears to me that most of the best bird photographers tend to use full frame cameras. Is there a clear advantage to full frame over crop cameras? I thought crop bodies would be best as they would give a distance advantage over full frame cameras but I fear I don't understand correctly. Reading Arthur Morris's web site is an example as it looks like he sold his crop camera and kept his two full frame camera. Any help you can give me in understand the advantage of full frame would be appreciated.

Thanks,
Randy Stephens