Casting Rotation comparing full Spell Speed BiS VS Normal BiS (Recommended using Ifrit Only)
Spell Speed Gear
http://ffxiv.ariyala.com/NK7T
A: 2.34s GCD
Bio, Mia, B2, SCSF, Ruin, Ruin, Ruin, Ruin, Bio, Ruin, Ruin, Mia, Ruin, Ruin, Ruin, B2, SF (2.8s), B, Mia, Ruin, Ruin, Ruin, Ruin, Ruin, Ruin, Ruin, B, Mia, B2, SCSF
(at this point it repeats itself)
VS
B: 2.43 GCD
B, M, B2, SCSF, Ruin, Ruin, Ruin, B, Ruin, Ruin, M, Ruin, Ruin, Ruin, R2, SF, B, Ruin, Ruin, M, Ruin, Ruin, B, Ruin, Ruin, Ruin, B2, SCSF
(Rotation has not yet repeated itself, but it has reached the 70.66 Seconds that Rotation A repeats at)
Total Potency of Rotation A: 5240
Total Potency of Rotation B: 4860 (This has 3% more damage due to higher Crit/Det, so equivalent to 5005)
So a difference of ~4%