Holdsworth 'Trentino' carbon....advice needed

[cougie uk]

Here's a few pics of the actual bike.
I am 5'8" with inside leg of between 30-31cm.
It is a compact geometry but it still looks smaller than a medium (i.e. I reckon 54cm is about right for me?)

That looks blooming tiny.

 

[Sloth]

That's what I thought....

 

[Sloth]

....and what I'm often told....