My understanding of the reasoning:
The 2007 and newer spec.B's have the 6MT which is heavier than the 5MT in the JDM GT. The AT is heavier than the 5MT, so front springs intended for the AT better match our heavy 6MT.
That being said, using JDM GT 5MT front springs should lower the front of our cars even more relative to the rear, which is also addressed by...
Our cars tend to look lower in the rear, and wagons are slightly heavier in the rear, so wagon springs lower the rear relatively less compared to the front, and the drop looks more even. Wagon owners are out of luck, which is one reason people make spring spacers to fix "saggy butt".
So using JDM GT wagon MT springs makes sense to me.
What I can't figure out is the difference between the JDM GT and JDM GT-B springs. Are the JDM spec.B pinks shorter or stiffer than the JDM GT pinks?