I test rode a Safire for an extended time. I ride a 15" and rode the small. I ended up with a small Gary Fisher (liked the longer TT) which is also a 15". I am 5'2", don't know my inseam but I am very short torso. FWIW even though my Fisher and the Safire are the similar size they felt very different so it may be hard to compare to your Marin. I poured over the size charts, Myka and Safire are different geometries not sure how different as it has been over a year since I looked. Can they order the Safire and not make you buy it? I was lucky my LBS would do this for me. They are a high volume shop and we are regular customers. My husband had bought a Stumpjumer FSR the year before.