@johnf3f - you are a brave soul to carry all that gear. the 800 is one fine lens so a congrats back to you as well! I think with shooter larger birds, the 600 was too much reach as I've cut off wings and other body parts on birds like Pelicans. it is as you as portray a top notch lens for smaller birds. if you have a link on flickr would like to see your work.
I managed to get my Canon 800 F5.6 pretty cheap and find it easier to carry than the 600 F4 I used to have. As you say it is a fine lens, though I do find F5.6 a little limiting the IQ, reach and lighter weight more than make up for this. As you say it is a great lens for smaller birds, attached is a Bittern I spotted this morning - it is unedited just JPEGed and scaled for web.
You are right that the very long lenses are not ideal for birds in flight. At the ranges where you can fit in a large bird then the image is degraded by the distance between you and the birds. More importantly I find it very difficult to get the bird in the viewfinder at all! For this sort of thing I use a Canon 300 F2.8 L IS, which is why I often carry both!
I actually have a Flikr account but am having trouble accessing it so no images up yet.