Let's not go through the Tervigon spawning vs. Gate of Infinity thing again. The rules aren't clear either way - GW has gifted us another ambiguous situation.
As for Doom - why would you replace Cataclysm? Especially with the blast vs. vehicle changes? I get that you lose D3 wounds when you use the power, but it's so much better than a 1/3 chance to get Iron Arm or Endurance.