However, you where fueling properly before you added a water/meth kit so my point stands. Aside from the heat generated from compressing the air, 50% more pressure certainly equals 50% more volume. See the Boyle's Ideal Gas Law. This is what allows us to generalize with forced induction engines so easily. All other things being equal, 2 atm you get two times NA horsepower because you ultimately get 2x the original amount of a/f into the cylinder to burn. Boosted hp is a direct function of NA horsepower. VE is irrelevant in these cases since we know the original horsepower.

"7psi out of a BW K03 is waaaaay less air than 7psi out of a Garret GT35, which is waaaay less air than 7psi out of a holset HX82" Can you give me any evidence to back up that claim? Its not the first time I've heard it and to be honest I've never found it to make any sense. Boost measured at the intake manifold is purely a function of air forced in the intake that exceeds the needs of the engine. That's like saying airing up a tire to 7psi with a big air compressor vs a small one will result in a different volume of air. If the compressor isn't big enough to supply the air, you wont get as much boost. The one thing that will matter is heat, and some turbos certainly generate less heat at equal pressures.

This is not a typical water meth system to cool the intake charge of an otherwise properly fueled engine, this is for all intents and proposes a stand-alone fuel injection system that needs to provide 45 HP of fuel peak. It will cool the intake charge as a byproduct and prevent detonation but that's just a side effect.