The muzzle pressure needs to be factored. The breech pressure may be 58,000 psi for any loads compared, but the muzzle pressure can vary significantly, and this is the pressure level that is popped off into the atmosphere to generate the sound level. This isn't a function of the bullet mass per se, but it depends on the powder burn rate and progressivity/digressivity, and of course on the barrel length. Generally speaking, if you want the quietest load while still having good penetration, go with a heavy-for-caliber bullet, load it with a fast-burning/digressive powder, and shoot it out of a long barrel with no muzzle brake, port or compensator. It will not be hearing safe, but it could be several decibels lower.
The heavier bullet will use less powder to achieve the same 58,000 MAP and therefore the muzzle pressure will be lower and the sound level lower.