It's my understanding that most shimano RD's have the same pull ratio. (Excluding certain models of Dura Ace). Meanwhile the FD pull is different.

I hear tale of Shimano making some FD's that are meant for crossing the gap, but someone else would have to chime in with their model #'s.

This is why Bar end shifters are usually used when converting between the two. The front shifter is friction only.