Impearls notes that Jackson modeled the Rohan on �horsey Vikings� and then writes a long and interesting article on the Sarmatians and suggests that they also could have been viewed as a model for the Rohan. Impearls also suggests that in the future he will look at other possible historical models for the Rohan.
Professor Bainbridge disagrees a bit:

…offers up a thoughtful argument criticizing Peter Jackson’s decision to model the Rohirrim after “horsey vikings,” and suggesting that the Sarmatians would have made a better model

Now in my reading of Impearls he seemed to say that not only was he not criticizing Jackson’s approach but, rather, was quite happy with it and that his intent is simply to look at the Sarmatians as another historical analogue that might have served as a model for the Rohan.
Read Impearls and decide whether the Sarmatians would make a good model for the Rohan. Bainbridge thinks not and provides a number of reasons.
Via Eugene Volokh.
Update(1/5): I belatedly correct the 3 misspelling of Sarmations. Having just read a book called Mars Crossing I clearly was hoping that Impearls essay was about a long lost Martian civilization.