Board Thread:Suggestions forum/@comment-26149161-20170406210456/@comment-31351354-20170407105821

A possible argument for the speed and endurance of the horses used by the Eldar, would be this quote from the Silmarillion:

"For from few their horses had increased swiftly, and the grass of Ard-galen was rich and green. Of those horses many of their sires came from Valinor, and they were given to Fingolfin by Maedhros atonement for his losses, for they had been carried by ship to Losgar."

- J.R.R. Tolkien, Christopher Tolkien (editor) "Quenta Silmarillion: Of Belerians and its Realms"