Since we can find such strong correlations between Gondor and "Basiliae Rhomaion",
it occurs to me that the Eorlingas deserve another look as well. Tolkien gave the Eorlingas the Anglo-Saxon language and culture, but he said that it was not really what they spoke (nor, perhaps, necessarily accurate in terms of their culture). We know that Anglo-Saxons were not nearly the horse-culture that the Eorlingas were. However, we do know that on the Russian Steppes there dwelt for many centuries Indo-European migrating tribes who periodically swept into more populated and developed cultural regions, such as the Middle East and India, and became lords in those lands for a while.
Obviously, Tolkien does not have the Eorlingas take over Gondor, for purposes of his own within the history of Middle Earth, but I can see a lot in the Eorlingas that are held in common with the Sakas, Sarmatians, Cimmerians, Aryans, (early) Medes, Parthians, and so forth. I'm left with the notion that Tolkien seems to have combined primary strains from both the Anglo-Saxons and the Indo-Europeans of the Russian Steppes.