Actually the difference Is minimal, within 100 fps, for both conventional bullet weights, so the difference on target is going to more dependent on bullet construction.
For years, mild steel bullets that have been copper plated have been available, out penetrating conventional copper/lead bullets normally.
Winchester white box 7.62 “Nato” loads use these bullets.
Now, add some of the various “black tip” bullets available and everything changes again. Having loaded numerous .308’s with M2 AP bullets, one can completely change the performance of the weapon by merely changing the bullet.
Then when we add the .308 to the mix, it gets even muddier.
Because the .308 can and is loaded to higher pressure and velocities, it can be more “effective” than the x54 or x51 choices, at least if the weapon can handle the difference. Some can’t.
Penetration tests can be interesting, at the same time it is not the end all be all want or need.
Choose your ammo accordingly.