I’d stick with the 40k Speciality plan as well. Eleven months is a very long time to train for one event however.
Looking at your timescale of two Builds and Speciality I’d be tempted to do a different Build and Speciality plan the first time around, if nothing else just for a bit of variety. The final build I’d do the Sustained Build and 40k Specialty but why not do a Short or General Build and a different Speciality Plan in the middle. Mentally it may break things up and train some different energy systems before focussing on the main event.