"Beggars Mounted Run Their Horse To Death"

Context: The Duke of York, with his sons and followers, is at war with King Henry VI. Queen Margaret has taken her army to the field, and with superior forces has routed York's men and captured York. When her men want to kill him immediately, the queen halts them, and taunts York. York, for his part, snaps back at his vanquisher. He calls her "she wolf of France, but worse than wolves of France." He derides the poverty of her father, who was "not so wealthy as an English yeoman." Then he continues his insults:

. . .
Thy father bears the type of King of Naples,
Of both the Sicils and Jerusalem,
Yet not so wealthy as an English yeoman.
Hath that poor monarch taught thee to insult?
It needs not, nor it boots thee not, proud Queen,
Unless the adage must be verified,
That beggars mounted run their horse to death.
'Tis beauty that doth oft make women proud,
But God he knows, thy share thereof is small.
'Tis virtue that doth make them most admired,
The contrary doth make thee wondered at.
. . .