The gain in improving a cartridge with lower body taper and higher shoulder angles is:
- Target capacity for bullets and powders available
- Less brass stretch, so less sizing needed, so longer case life
- Improved internal ballistic efficiency, because more powder is burned in/near the chamber, instead of merely adding to bullet mass(increasing recoil and muzzle pressure)
If your talking throat erosion as a matter of flamepoint setup by shoulder angles, I don't know that this has been tested & proved beyond notion. But I don't know of anything 'bad' in higher shoulder angles -except for feeding. You might want to consider feeding, as not any ole action does this well with improved cartridges. At 40deg you may need single shot feeding, even with a coned breech.