Short answer - none. As long as the methods are linear then a % pressure change due to a charge change will yield the same % in another method.

Hodgdon gives most loads in CPU and Birmingham Proof House uses tones. I think tones times 2200 is close to PIS, not certain.

When working up a load for my .375 I pick the one that was the LEAST, and then reduced it 10%.

One think I have noticed in published pressure is that the last 2-300 fps requires non-proportional pressure.

Accepting 2300 fps instead of 2500 in a .375 knocks close 10% off the pressure.

Modern bullets work well at lower velocities and for short range hunting, why not reduce velocity and save you double rifle.