If you use forces correctly Khergit are awesome. Keep your men closely packed, let the enemy straggle out to you, lead one charge and then pull back. If they don't have many archers sit on a hill and fire at them. *shrug* I have fought off armies 3x my size or so with a good mix of Khergit.
EDIT- I also disagree about Vet Archers, they seem to do well and SURVIVE a lot better than lancers.