My questions would be more about how it feels. If the relationship between the seat and bottom bracket feels right, does your upper body feel cramped? overstretched? relaxed?

Everyone has different proportions, and trying to fit a bike based just on height is simplistic---a place to start but really of limited value.

As [MENTION=426453]OrenNoah[/MENTION] notes, better to be a little small than too big. You can add spacers, a longer seat post, a set-back seat post, a longer stem ... but you cannot shrink a frame which is even just a little too big.

Another thing---a lot of people look at stack and reach, but also look at seat post angel and setback. Pushing everything forward might relieve a cramped feeling but might not be comfortable over time. The relationship between where you sit on the saddle (where you actually sit, not the nose, as some people suggest) to the BB is really important. Everyone has a compromise between maximum comfort and power and efficiency---some angle to bend forward, some hip angle, and some relationship between center of gravity and pedals, where they feel the best--stable and able to rid as long as they want. Adding a little seat-post setback might be better than just adding a honking huge long stem.

Only you can tell if you are comfortable on a bike.

i will say this---I have several bikes and while a few are nominally '56" as in 56 cm virtual top tube---none of them actually are the same size. I also ride a couple much bigger frames, and a tiny frame, and they are all comfortable because I have adjusted all the contact and control surfaces to suit me.

The only issue I can see with a too-small frame might be toe-overlap. And that I don't find to be much of a problem, as it only happens at extreme steering angles which only happen at extremely low speeds.

However ... and this is based on purely nothing, just pulled out of thin air ... it looks to me that you could fit well on a medium. Fewer spacers, same stem, shorter reach bars, less exposed seat post, and the same control and contact points.

The extra few cm reach would make a difference. The much taller head tube would make a difference--and might lessen actual reach because the bars could be higher if you added spacers (with the spacer stack you have now--could be 20 cm? that's about where the M-frame head tube would end.)

Are you uncomfortable on the bike now? besides what people are telling you, and ignoring the numbers, do you feel okay on the bike?