Looks good. The image fills the screen, but some may have the image flow off the edge of their smaller computer screens. I've had success with Large 1024 x 683.
I've been doing this posting from my flickr recently too and have gotten favorable comments. The large size picture choice seems to fill the screen best. It may be my imagination, but the pictures posted from my flickr account seem to me to be better quality than those posted directly from my computer.