They are super stretchy, so I think they run big. I am a 4 in Banana, a 28 in COH and Sevens and I wear a small. My brother's girlfriend tried on my small (she is an 8 in Banana, a 29 in COH and Sevens) and they stretched to fit her well......
i don't have those particular gauchos but i do have the ones i think tara is talking about. i am about the same size as tara as well and i feel like a small is just right.