Depends almost entirely on hit geometry. Assuming fair hit: If its near the edge, the backface deformation and impulse could cause a similar wound as getting a hard small surface strike from a martial artist. Which means it depends on whatever protection you have underneath the plate, and where exactly you got hit. A gut punch or a collarbone chop are the comparison. For a center hit, both slugs and rifle rounds can crack plates, and the impulse alone will injure. Cracked ribs, broken sternums. Like a expertly done front punch, it will put you on the ground minimum. Other less likely but possible injuries include pneumothorax, hernia, heart failure, assorted internal bleeding, compartment syndrome.
Casualty statistics from Iraq/Afghanistan War and leaked FBI guidance on SWAT raids indicate that center mass fair hits 12g slug or full power rifle (30-06, 7.62*54R) into plate guarantees the officer is a casualty. They cannot operate. Survival rate once evacuated is 95%+ but will be out of action for weeks or until the chest bones heal.
They dont make body armor good enough to make you an unstoppable robocop tank. They do it for repetitive replacements, insurance and medical billing, much more profitable.