Wove’s rules above are pretty much exactly as I’ve always though rail movement should be.
I might be a little more generous to Turkey and allow it to rail anywhere within its original tt; they did have a railway all the way to Medina, and were building one to Baghdad.
Preventing the CPS moving units from Berlin to Baghdad would be a vital strategic goal for the Allies, definitely spicing up the battles in the Balkans.
Also consider how big some of the SZs are on this map: you can ship from Canada to Marseille in one turn. This is how the Allies can move units, the CPs have to march overland one space at a time, when in reality the trains would get them to just behind any front line in no more than a week or so.