The 5.7x28mm round is inferior to the 9mm round with regards to wounding capability,it may punch Armour but it does virtually no significant damage to soft tissue.The bullet tends to yaw almost immediately upon entering soft tissue and does not penetrate the required distance to reach the central nervous system or major blood vessles.The 9mm is a much better round with regards to penetration in soft tissue as it will get into the body to reach the vital areas.The only real advantage the P90 has over the MP5 is in its large magazine capacity,of course you will need those extra rounds to do the job.
The FN Five Seven offer even worse performance than the P90 in soft tissue due to it's lower muzzle velocity.....Try doing some reasearch on the matter ,not reading FN product brochures