Yeah confusing is the fact that they say actual frame size is 56, but then seat tube length is 53.3 without seeing a diagram it's hard to say what they're measuring from, I think the size 56 is more of a virtual size because the bike does have a sloping top tube.

In any case I ride an older pinarello which has a seat tube that, measures 55.5 c-c; a 56 top tube and a 160mm head tube. Based on that info since I like that fit I would select the 56 motobecane for my height as it most closely corresponds to geometry of my current frame, even though my frame has traditional horizontal top tube (non sloping) geometry-the effective TT is the same, and the head tube is close.

I think BDs height chart seems pretty accurate to me. I would check your measurements again, but am fairly certain the 58 will be too big. Also remember these frames look like they have a fairly tall head tube (170 on a size 56) so if you are more inclined to racing or fast sport riding, the 54 may even work for you.

I see they also provide seat post height recommendations, which is nice. Work out your seat post height with an online calculator and see where it falls in the range of recommended min/max heights, that might help you as we'll. if your at the extreme max/min end of that range you may want to look at next size up/down. Standover is less of an issue with most road frames today, provided your junk clears top tube, stand over clearance is a more critical factor with track, cyclocross and mountain bikes.