I'd be happy for TBS or GermanJoey to burn an Engineer to rush the Pentagon. We'll get plenty of advance warning about anyone else trying. Adding the Aqueduct and Ironworks only adds four turns to the build, so lets decide if we want it once we finish the Ironworks. We might have a juicier target by then.
With Ironworks
52 hpt *1.25 = 65 hpt into the Factory (250 hammers) = 3.84 turns
52 hpt *1.5 = 78 hpt into Coal Plant (150 hammers) = 1.92 turns
52 hpt *2 = 104 hpt into Aqueduct (100 hammers) = 0.96 turns
52 hpt *2 = 104 hpt into Ironworks (700 hammers) = 6.73 turns
52 hpt *3 = 156 hpt into Pentagon (1250 hammers) = 8.01 turns
Total = 21.46 = 22 turns
Without Ironworks
52 hpt *1.25 = 65 hpt into the Factory (250 hammers) = 3.84 turns
52 hpt *1.5 = 78 hpt into Coal Plant (150 hammers) = 1.92 turns
52 hpt *2 = 104 hpt into Pentagon (1250 hammers) = 12.02 turns
Total = 17.77 = 18 turns
The other cities that could build it are Xigua, Watercress, Carrot, Endive or Leaves, all of which I'd like to get Factories and Power Plants in first. X and L are fully grown, C and E are about ten turns from being fully productive and W is a hybrid so probably wants commerce multipliers rather than wonders.
BTW - I was wondering about putting Jails in our bigger cities before attacking Pindicator, but actually we've got a pretty good happy cap in most of them, so it's only the places we're drafting heavily that are likely to suffer. And most of them don't have the hammers to build a quick Jail
. City list from t192:

With Ironworks
52 hpt *1.25 = 65 hpt into the Factory (250 hammers) = 3.84 turns
52 hpt *1.5 = 78 hpt into Coal Plant (150 hammers) = 1.92 turns
52 hpt *2 = 104 hpt into Aqueduct (100 hammers) = 0.96 turns
52 hpt *2 = 104 hpt into Ironworks (700 hammers) = 6.73 turns
52 hpt *3 = 156 hpt into Pentagon (1250 hammers) = 8.01 turns
Total = 21.46 = 22 turns
Without Ironworks
52 hpt *1.25 = 65 hpt into the Factory (250 hammers) = 3.84 turns
52 hpt *1.5 = 78 hpt into Coal Plant (150 hammers) = 1.92 turns
52 hpt *2 = 104 hpt into Pentagon (1250 hammers) = 12.02 turns
Total = 17.77 = 18 turns
The other cities that could build it are Xigua, Watercress, Carrot, Endive or Leaves, all of which I'd like to get Factories and Power Plants in first. X and L are fully grown, C and E are about ten turns from being fully productive and W is a hybrid so probably wants commerce multipliers rather than wonders.
BTW - I was wondering about putting Jails in our bigger cities before attacking Pindicator, but actually we've got a pretty good happy cap in most of them, so it's only the places we're drafting heavily that are likely to suffer. And most of them don't have the hammers to build a quick Jail

Completed: RB Demogame - Gillette, PBEM46, Pitboss 13, Pitboss 18, Pitboss 30, Pitboss 31, Pitboss 38, Pitboss 42, Pitboss 46, Pitboss 52 (Pindicator's game), Pitboss 57
In progress: Rimworld
In progress: Rimworld