I'm 5'2" and ride a Small Safire Expert. The fit is great, but if I was much taller I feel like I'd want to size up to a Medium. The Specialized sizing chart has held true for me for both road and mtn bikes, and at 5'5" it puts you squarely in the Medium range.

http://specialized.custhelp.com/cgi-...344668&p_olh=0

That said, is there another shop nearby where you could test ride a Medium Safire/Era/Myka FSR before you order?