If your seat tube, measured from the center of the bottom bracket spindle to the center-line of the top tube is 53cm, then I would say it is a pretty good fit for you. However, how can the center to top measurement be 56cm? I am a bit confused. Also, why would you report seat tube measurement in metic and top tube measurement is imperial terms?

Generally, I also offer my online customers a stand over height and suggest that they compare that height to their inseam measurement(riding shoes on). If there is between one and two inches clearance between the tube and your crotch, the fit will probably be OK.