Plates to me are all or nothing. How do you know the threat is shooting M855 vs M193 or generic 55 gr FMJ? Take a poll? Start a pool? Ask him nicely?
Your plates should stop the common threats in your AO.
There is theory and reality. Most guys are going to attend patrol level gunfights in what they are wearing when they hit roll call. That is reality.
Barricade suspect with multiple responding and a staging area? Different story.
I would focus on the lightest plates that will stop common threats in a shape that can be worn all shift. That takes dollars, which are finite.
As ambush type OIS increase, you need to be wearing what will improve the outcome of a common ambush.
Bottom line, if there is a program that will put better armor on your cops, make use of it, even if it is not your dream package.
Any hard armor is better than the awesome stuff that nobody bought because it was too expensive.