Your measurement issue seems similar to my son's, and he rides a 54cm Roubaix. Resist the temptation to go larger just because some chart says you can do it - fit is a personal thing.

I think the best answer is to ride both before taking the plunge.

My son had a year's experience riding a 56cm, and the neck/shoulder and overall sloppy handling problems it created, which lead him to the decision to go down a size.