I’m 5ft 10″ and I have a just received medium sized full bike. I ordered the flat bar as a commuter bike with a view to sticking drops and shifters on at a later date along with some knobbly tires for some CX/Adventure.
Compared the geo against my 54cm Supersix Evo, which fits me perfectly and the medium London Road looked the closest match. I know the Supersix is race geometry and this isn’t a race frame so I looked for the few measurements that were most important to me.