This is the biggest interval I can manage (e.g. C->E, although I can't possibly reach say C#->F [EDIT: Of course, that's an 11th so that makes sense...] but thankfully it's also the biggest interval I've seen in sheet music.
The thing is, it hurts to do this and a piece I'm learning has a few of these in it. If there's one thing about pain+piano I know: If it hurts--don't do it.
So, other than for people with Rach' hands, is this supposed to hurt? With practice is it possible to enhance your stretch?