What is a practical level of armor?

Level 4 is some of the toughest stuff out there, it's also the heaviest. This could be a pro in that there is more mass to help dissipate energy of smaller rounds but the weight, the rest of the time your not being shot, would be rough.

There's lightweight 3a armor which wears more easily, but with less mass each round that connects will deal massive damage. Not to mention the fact that higher velocity rounds will punch clean through it.

the plates in question will be curved 11x14 AR500 plates.