At 5'6" riding your current 54cm Trek...it sounds like you might have a long torso and short legs, which could mean that you don't necessarily need a WSD bike. Most WSD bikes are designed for short-torso/long-legged women (like myself). I'm also 5'6", but I ride a 51cm Cannondale Synapse. I also have a 54cm Trek 2.1 WSD as a "back-up" bike, but it's slightly too big for me so I only ride it when my C'Dale is in the shop. So you may want to expand your selection to some of the "unisex" bikes out there.