Koyuki:

Ruin III is definitely a possiblity and I'm sure I would weave it in a few spots. The main problem with Ruin III spam in Bismarck Ex is between all the Tornados and Water spouts that spawn on your face, it's best to keep it mobile as possible. Hence the Ruin II spam. And yes, I ofcourse auto attack.

As for saving the DPS CD's for the Sanuwa, I was told that if you cannot get down the Carapace in one go, then you'll struggle on the Sanuwa, hence why everyone pops their CDs on the Carapace.

I use food, though I wasn't using potions and poisons at the time, so naturally using artificial consumables, I could ofcourse improve my DPS in that aspect, but it's more so how my rotation during the fight itself.

I don't think my rptation is near perfection at all, but I feel like I've stretched it to it's limits. So unless I'm doing something glaringly wrong, I can't see a huge DPS increase in doing anything differently. (Aka, Ifrit may or may not increase my DPS in that phase due to radiant shield affecting both tanks and the adds not moving in the slightest. But would that DPS increase be worth dropping the Contagion on the second untouchable add that I cannot hit?)