I swear there was some experimental munition nato was working on for 7.62 which punches L4 consistently but I got the name wrong.
M993 is the standard 7.62 NATO AP round for the US military. M1158 (which i have witnessed penetrate and put down targets behind concrete walls) is the advanced AP cartridge that is in very short supply and ultimately was dropped when Navy SW opted to move to .338 Lapua Magnum and standardize on it while more conventional SOF kept up with Mk 262 (for 5.56 NATO precision rifles), and later the Mk 318 (for USMC Raider teams, now called CSO teams). Mk 316 was adopted for precision long range 7.62 NATO shooting and also has light barrier penetration ability but it's really more of a military-optimized Federal GMM round. my experience with the Mk 316 is with the Mk 11 rifle, and i would rather have the Mk 248 in .300 Win Mag if i had to reach out and touch someone.
depending on secret sauce ammo is probably not ideal. craft your battle environment and use volume of fire to establish control and overwhelm, to use 7.62 with a transferable MG loaded with AP to crack open armor after a mag dump at close range. if you're opting to stop the encounter at a distance, spending money on .50 BMG API (called "M8") and learning the skills needed to handle that rifle at the engagement range you need to work it in to stop a vehicle or something is what you'll do.
there isn't anything magic that will penetrate level 4 plates in single shots that is reasonably man portable. either use a large heavy weapon, or rely on repeat shots or focus on just avoiding the armored portions of the enemy body. i'm not sure you understand this, as it's been outlined several times.
there isn't anything you're buying that'll do the work itself and getting the "right thing" is less important than developing practical skills in movement, maneuver, tactical thinking, and manual of arms. getting good with a typical AR-15 will see you through a
lot of encounters even with body armored enemies (like how soldiers are doing around the world today in multiple conflicts). optimizing those skills with particular training comes next.
if people telling you from their own experiences how to work around the problem isn't convincing you to drop your hang up on level 4 plates, i'm not sure what sort of advice you're really asking for.
as per my blue book, P is 1993 transitional.