Let's talk about 6x30 Ork Boys, because you can't get more hordy than this.
Imothek: 2.92 Ork Boys dead per shooting phase as long as it's night.
Worldscape in First Turn:
30 models will fail the test and 24 of them will die because they failed the save.
So for 610 points you killed 161.52 points of Orks.
For those points you could also take 3 Doomsday Arks.
They would kill much more Orks and wouldn't be a waste of points
It's a great combination, but in my opinion it's too expensive and I would never use them outside of Apocalypse-games.