Lovely builds in here guys (and lady). I am looking to pick up a 721 soon and build it up but have a question of sizing.

This is the current bike I have in a sz 55
http://www.raleighusa.com/archive/20...back-alley-12/

After looking at retro-gressions website, and the geo, I am wondering if I should get the 53 or 55 721. Any help would be greatly appreciated