Used 5DM1 vs 50D

They are two different cameras. 5D for landscape, portraiture, studio and 50D for sports, birding and actions. From your description and lens' collection, it seems 5D works better for you. There is a similar thread in this forum that you can check

http://forums.dpreview.com/forums/post/50864596

BTW, you need to take account sensor format (that is still #1 decisive factor) into amount of pixels. 12.8mp FF 5D with a sensor twice bigger still outresolves 15mp 50D easily if you frame the subject into similar FOV by moving closer such as in portraiture case or by using longer focus-length lens such as in landscape case. 50D has pixel density advantage (or "reach") when you unable to move closer or doesn't have longer lens such as in birding case. 50D has also better LCD and faster burst rate and cross-type outer AF points that make it more suitable in action shots.

--
http://qianp2k.zenfolio.com/