I've been reviewing the Pact changes...haven't had a chance to test them, but here are some thoughts I've had...
First, I think the Missile Pact needs to affect phase missiles differently...currently it increases their chance to bypass shields by 15% (which is a huge boost)...I think that bonus should be changed to only increase their damage by 15%...
Second, I think the new changes to sacrifice may be too powerful...this is essentially the same cultural impact as a deliverance engine, yet it is done by a simple cruiser....now, understandably, the player does have to sacrifice a ship (and the time it takes to replace the envoy) and the "culture bomb" affect can't be used on enemy planets and the ability doesn't stack and it prioritizes old buffs (so it is harder to keep it going continuously without constant micro)...so, those are a lot of restrictions...but I really don't think a player should be able to continuously produce 5 culture (the same as 5 culture centers) on a planet by just building a simple envoy once every 150s...
You could use the envoy on one of your own planets (a border world) and essentially culture flip the enemy planet with little sacrifice at all...in fact, all it would require is the cost of the envoy cruiser once every 150s...since the ship is destroyed you wouldn't even constantly be needing the 12 fleet supply, and even if you did, that's a small price to pay...your enemy is losing a planet while you are doing virtually nothing...
I like the shock effect of this, so I think the culture bonus of 5 is good...but the duration of 150s, that seems a little too long...I can see this ability being abused, and I don't think any envoy bonus should be even close to that level...I'd recommend reducing the cooldown time to 90s...
So, to sum it up, I'd make the missile pact increase PM damage instead of % chance for shield bypass...I'd also reduce the duration of sacrifice from 150s to 90s...