“Hyborians” are composed of a great number of civilizations such as the Aquilinians, the Corintians, the Nemedians, Brythuntians, Kothians, Ohirians. None of these are even remotely based on the Russians.

The Hyperborians are a more barbaric people from whom the more civilized Hyborian nations all decended from. Again, not really fitting.

To a degree that is somewhat accurate. Look at the vast swath of land the Hyrkanian’s occupy, and the simple fact that the Turanian’s themselves ARE Hyrkanian (and not even remotely Mongolian but more Ottoman Turk). The Hyrkanians are not one single people even though they may have started out as one (the decedents of Lemuria enslaved by the Khari and after thousands of years of enslavement [and no longer remembering their Lemurian ancestry] they rose up and destroyed their former masters causing them to flee [which in turn caused the Khari to eventually fall upon the Giant Kings and take over Stygia] ). But as they spread out over this massive landmass they would have incorporated many different peoples into their own and yes, the ones closes to Khitai would be very much based upon the Mongols the ones on the other side of their teritory closest to the Villeyet Sea would be very different than those.

Thus, the most logical choice would be the Hyrkanians.