I’m also 5’9” and ride an Arkose medium. Stock short stem and setup also road bike style with a low front end (saddle is also cranked forward). Think I’m almost between sizes and I sometimes reckon I could have gone with a Small as it is a long bike, but in the end I do definitely think M is more my actual size. I’m don’t feel too stretched out on it at all.
I’m also 5’9” and ride an Arkose medium. Stock short stem and setup also road bike style with a low front end (saddle is also cranked forward). Think I’m almost between sizes and I sometimes reckon I could have gone with a Small as it is a long bike, but in the end I do definitely think M is more my actual size. I’m don’t feel too stretched out on it at all.