Randy - I think that sounds fantastic. The only downside, if one would like to call it that, is that your 20D set up will yield almost the same field of view.
20D + 200mm + 1.4x = 448mm focal length equivalent, compared to full frame.
5D + 500mm = 500mm of course.
Now the plus side, is that the 5D + 500mm/4L-IS will yield absolutely stunning images when you're not "reach limited". Image quality wise, that combo is basically the top of the chain.
When you do become reach limited, swap the 500mm onto the 20D and you will project many more pixels on the subject that way.
This is basically what I do, and it's the only reason for keeping around the 40D. Sometimes the 1.6 croppers pixel pitch/density is useful when I need maximum reach. Otherwise, I always use my 1DmkIII.
While I was in Jackson Hole this weekend I walked into many photography shops, and several of the pro photographers said they used that exact combo, 5D + 500/4.
You really can't do any better. Man, I'm excited for you... I need to go buy a new lens now too
Rob
