If slihouettes are your game, you have the wrong load. The silhouettes go down by momentum transfer (M x V), which is why a 125gr .357 wil ring them and a 240gr .44 will slap them down. It is ballistically easier to add 50% to mass than 50% to speed, and easier on the gun.

Some silhouette shooters shoot what are nearly proof loads (10% over)in their guns, which materially shortens their life. I believe the 42,000 PSI you cited is the "definitive proof load" which is 20% over the rated working pressure. This is the max load the gun design is required to sustain (once) without flying into pieces, and is not a safe working load by any standard.

You might factor in the early replacement of the gun as part of the overall cost and see if light and hot loading is really cheaper.

By the way, you are right that PSI and CUP cannot be converted from one to the other accurately, and are measuring different physical data depending on case size & shape, and powder used.