That's great info. When I was saying level III is not rated I was not including Level IIIA (still questionable) or Level III + (which I trust to stop 5.56).All level III composite armor is not created equal. There is Level III + armor out there that will stop mulit hits from 5.56 M855 and M193......but you are going to pay a premium for that kind of protection in a 5 to 6 lb plate.
The advantages of level III composite armor is weight reduction and mulit-hit rating, along with durability (depending on plate composition) against dropping banging against hard surfaces. The disadvantages are inability to stop 30 cal AP, sensitivity to heat/cold (Above 150, below -15 degrees) and prolonged UV.
The advantages of Level IV armor is single hit rating 30 cal AP protection (although I have seen a level IV plate take four 30-06 AP hits before it failed). The disadvantages are weight (though not quite as heavy as steel) and damage (micro fractures) from drops/banging against hard surfaces that can greatly reduce the effectiveness of the armor and as a result it should really have an annual x-ray to asses that.
The advantage of steel armor is reduced price....and just about nothing else.
Having worn worn both Level IV and Level III enhanced for extended periods of time, I would choose a bouncer with level IIIA soft armor and Level III enhanced plates any day and accept that if I get hit with a 30 cal AP round it's just my time. For me he reduced weight and increased maneuverability is worth the reduction in protection. In fact it's exactly what I have, Eagle Maritime CIRAS with Speer BALCS Cut Level IIIA soft armor and a MSA/Paraclete DHP3-1012 triple curve. Pricey rig for sure, not for everybody, but worth it to me. As always, YMMV.
I think what you have done is a very good balance. Especially when you consider that .30 AP ammo is pretty rare with civilians, but the 5.56 Perpetrator is all over the place and is actually some of the least expensive 5.56 out there.