performance difference between short cage/medium cage Campy rear derail.

Hello

upgrading from 8speed Chorus to 10 speed Record and trying to educate
myself to the different cage lengths for campy rear derailluers. I want
to run a 12-25 cassette and from what I read online about cage lengths,
the Campy short cage length would work fine, being able to throw the
chain to a 26t while the medium can throw the chain up to a 29t(if I
remember correctly). Other than this, any difference in performance
between a short and medium cage length? I don't expect to use anything
higher than a 26t as that my local bike shop recommended the 12-25 for
the terrain around where I live....I would think someone would use a
medium length cage so to use a more variety of cassettes...thanks in
advance for your advice/info
-Mike