The problem with 806, quite frankly (ha ha, good pun, no?) is Charlemagne. Such a vast swathe of Western Europe under one central rule, IMHO, would be problematic. The same sort of feudal simulation as one should (hope to) find in CK just wouldn't apply. Vassals, for instance, were incessantly watched by Charles' missi dominici. To start it somewhat after Charles' death and the demise of the administrative system he established, now that might prove worthy of simulation.