As a speed runner, I explored nearly every option.. I would like to share this.

If you are using swiftcast as your opening on a WHM, you are making a huge mistake. If you honestly want to maximize the efficiency. I'll have a tip: none swiftcast holy followed by immediate swiftcast holy will overwrite 4 sec CD on previous full potential holy. Example: you cast holy then timer begins to tick, 4 sec.. 3 sec.. 2 sec.. swiftcast holy lands, back to 4 sec. Here is the best rotation: Holy - swiftcast holy - assize - (GCD refresh at this point) - Aero 3 (monsters are still stunned) - shroud (it heals lost MP from Aero 3 before spam begins) - SoS - Holy, Holy, Holy.. Remember, it doesn't only rewrite, but the kind of damage you can pull of in short period of time is massive: it's a par with flare, in terms of damage, speed.