The numbers are hard to compare as one is SAMMI standard and the other is European (CIP I believe). I think they may measure from different spots on the case even though they are both measured in PSI.
You would need to measure them both by the same standard to be able to compare them to one another fairly. Are any Western Manufacturers making commercial x54 now (Winchester, Remington ect) if so they have SAMMI data on their rounds and can compare directly to the .308. All my x54 is European! Even the commercial stuff I have.