I have spent some time in Portland, ME. You will be fine all the way up with a 56 running an 18 rear. Just be careful, when you get that big some rings go to aluminum and those wear way faster. Don't try and bike up to Camden with that ratio though, unless you have robo legs, that hill will massacre you.

I droped to 48/12 for better acceleration out of lights where I moved to now BTW, still flat, just WAAAAAAYYYYY more traffic.