Panda, two points:
1. I agree that a 54 sounds a bit small, so sight unseen, I'd say 56.
2. The best way to resolve this is a test ride -- try a 54, then a 56, in the bike you like. If they don't have both in your choice, you can either try the closest thing they DO have, or try another shop.
Some bike fitters, for some reason, come up on the small side when they measure somebody. Follow #2, and you should get a good feel for where you really are. HINT: a proper-sized bike just 'feels good' to sit on, coast, and pedal on. It's almost exciting, like the feel of the best pair of shoes you ever tried on.