I'm 5'11" too and I've been successfully on a 54, 55, 56 & 57. I 53 might be a bit too small. Did you get specific measurements of the top tube?
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A conclusion is the place where you got tired of thinking. - S. Wright
Favorite rides in the stable: Indy Fab CJ Ti - Colnago MXL - S-Works Roubaix - Habanero Team Issue - Jamis Eclipse carbon/831