3a is inferior to 3
The armor gets better the higher the number is, and the 'a' designation really means a weaker but more compact version.
Most people find 3 to be too thick so they go with the slightly weaker 3a.
Now, the issue is vests wear out over time, so different brands can all stop a bullet equally well when new but 3 years later some may be weaker than others. Unfortunately the longer lasting ones are generally more expensive.
Further, not all body armor covers the same amount of body. The standard type covers the front and back, but the sides are open. Some add side-panels and others are full-wrap.
http://www.qmuniforms.com/Brands/Second-Chance/Body-Armor/Second-Chance-Summit-Full-Wrap-Level-IIIA-Body-Armor.axd?utm_source=GPS&utm_medium=organic&utm_campaign=GPS
THAT is good armor...and it is expensive
Second thing is comfort. Second Chance body armor is a tad heavier than most but it is also more comfortable than most
here are more specs
http://www.safariland.com/bodyarmor/Summit.aspx
HOWEVER, for the price of upgrading from the issued armor to the 'best' armor, I'd instead suggest you have your boyfriend keep the standard issued armor and spend the money on a tactical combat class.
Here are some of the best
http://www.thunderranchinc.com/
http://www.gunsite.com/main/
http://www.sigsaueracademy.com/
I would avoid Front Site training. there are some....issues there.