You're reading the wrong number.

You fit a bike (in most basic fitting) by the effective top tube, so that would be the 56cm with the 57cm top tube, and maybe the 58 with the 57.9cm top tube (but at 5'11" the 58cm is less likely). But that bike has a steep seat tube angle. If you need lots of setback that may be a problem without a high setback post - oh nevermind, your setback is short. There are lots of variables to look at in a geometry table and not all bikes can be tailored to your ride characteristic requirements.

Also, I caution anyone buying a bike that asks for a size through an internet forum and doesn't understand a fit calculator and geometry tables. Perhaps do a lot more research on the subject or get physical fitting help.