The overall size is different in all respects. I generally use the small stakes on 3 person tents and smaller and the medium stakes on 4 person tents and larger. If you're concerned about weight at all, the small ones can do everything the medium ones can, so you can shave weight on even larger tents if needed... They are nearly the same in size though, it's not a huge difference either way.
Eric V Chri,
I have the Rock 22 2 person tent does that make a diff..
CHRIS C Eric, I would recommend the smaller stakes for that tent unless you will be somewhere with higher winds... Any wind issues, go with the larger ones.