Just to pick up on this bit RJ, you can't repeat the mission, until the last one has worn off, so I think you could only poison the same city every 7 turns, even with unlimited spies. Unless Firaxis are changing the equation to 6

every turn for 6 turns with no declining counter, thats still only 36

. If its as it is now, i.e. 6

, then 5, then 4, then 3, then 2, then 1, most cities will probably be growing after the 2nd turn of poisoning. Small cities in large empires with many health resources won't be effected at all. Even repeating every 7 turns, won't really have any effect in the long run, I'd suspect most cities would still v slowly grow.
As an earlier poster said, if the ai likes to use it EPs on what will become virtually pointless missions, thats quite an advantage over a human who won't bother, apart from maybe extremely particular circumstances.
If the mission cannot harm a city because it has a too high food surplus or a too high health surplus, then that is equal among game speeds. If the mission isn't causing harm because of the food storage, then you should compare 3 consecutive marathon missions with 1 normal speed mission. You do have the spy points for the missions at marathon speed as you have 3 times as many turns to gain the spy points.
If you think the mission is too weak in general on all game speeds, then maybe you're right. But on the other hand, you shouldn't use the mission on a city with a good health surplus that is still growing.
It is probably fair to worry about the AI. As I see it, 3 consecutive poison water supply mission at marathon speed equal one poison water supply mission at normal speed and without additional AI coding, I don't think the AI will do 3 consecutive poison water supply missions on marathon speed. That requires planning and the AI doesn't really plan a lot. Normally its decisions are about what is best in the present situation.
Even a human player who is planning this might fail as the second mission that was supposed to be consecutive might fail and thus there might be a few turns for the city to recover from the previous mission.
We actually shouldn't mix up the poison water supply and ferment unhappiness missions. I guess that a 6 strength ferment unhappiness mission is about as strong as an 8 strength poison water supply mission in most situations.
By the way, in general (independent of game speed) these two missions are at its strongest when they are performed multiple consecutive times against the same city. This is because when the city is low on food storage after the first mission has succeeded, then it is most vulnerable to another mission. So maybe the AI should try to get the most out of these missions by repeatedly hitting the same city. That would also help any weakness that the AI might have with the marathon version of the mission.
Other differences between the game speeds and the new spy missions as described by alexman:
- At marathon speed you might be able to harm a vulnerable city significantly with 2 consecutive missions and a third mission would be superfluous. On normal speed, the same result would be reached by a single mission in this situation and that would thus be relatively more expensive.
- At marathon speed, you have more time to move your workers to the city that was attacked in order to change tile improvements and reduce the damage from the consecutive missions.
- You might place a spy in a city that was attacked by one of these missions and that would thus make it easier to protect your cities against serious harm at marathon speed. You will only suffer serious harm at marathon speed when multiple consecutive missions succeed.
I don't think the missions are perfectly scaled by removing their differences and making the marathon speed mission relatively cheaper, but it is also not a horrible scaling method. If the AI can deal with it, then I think the scaling method is about as good as the -6 health for 3 turns, -5 health for 3 turns, etc. type of scaling suggested earlier.
By the way, I've been arguing a lot about marathon speed in the various posts in this thread, but I don't even play at that speed setting. I'm an epic speed player. Just arguing for a better game in general, I guess. Marathon speed is just the most deviant speed setting and thus suffers the most from any errors in game speed scaling.