Have you of you guys found or tried some monsters/dregs of humanity/minions from DH/RT and translated them into Hordes yet? Any particular ones you'd found that would be a perfect for being a "horde"? Also, found any hordes of monsters that would be perfect for DH/RT? (I found a Horde of Gloom Haunts ready to infest the ship the PC's are on :3 )

Well the various types of Zombie that inhabit the game would be a good start. Orks would make a pretty good challenge as well I'd think, given how tough they are.

BYE

A horde of grox followed by a horde of Slaughtermen with their chainswords could be fun.

I would say Eldar for some hordes. Not a Magnitude of 20 or 30 but a magnitude 10 for the more ranged types like Dire Avengers.