Just my 2 cents. I do not have as much knowledge as some here on this site.
1) Do not buy AR500 steel plates. Although they will handle up to .308 win ball ammo (7.62x51 Nato) there is bullet
splatter involved.
2) They weigh in at about 8#'s for a NIJ III+. Then there is the weight. 2 x 8 lbs = 16 pounds. Now you know why they
are inexpensive.
3) Ceramic plates absorb the bullet and much of the energy so there is less body trauma and little if any bullet splatter.
They also weigh in at around 4 #'s or less. I would rather carry around 8 lbs vs. 16 lbs.
My set-up is two ceramic plates (front and back) with III soft armor behind each plate. This adds only ~1 lb per side but really helps in diminishing the trauma you will experience when your ceramics are hit PLUS the added protection adds up to and including .30/06 ball.
Now of course you could use the soft armor behind your A500 plates but you still get bullet splatter plus now your body armor weights ~18#'s. YIKES!
This is the company I have dealt with and have been happy with.
In closing: Save your money and buy ceramics with backers rather than buying AR500 steel plates.