I am 5'6" and those fit calculators put me on a 52, I had a Redline 52cm but I just feel hunched over on it and did not care for the longer stem and the twitchy feeling that resulted. When I bought my current bike the LBS owner said 52 was not a good choice and put me on a 54. It's hard for me to think of a 6' guy on my bike. You could go see what size a decent shop would put you on and determine from there if you should send it back or maybe just get a good fitting done.