I think you should consider leaving the bumpers alone - stay with the Euro bumpers.
If you are talking about your personal safety in the car, the US bumpers are not much more in the way of protection. That is, the car frame and body are going to be what protects your body, not the bumpers.
The idea behind the USA bumper specification is to absorb a 5-mph impact with minimal vehicle damage. It has little to do with protecting the passengers in a major crash.
If you have a big crash, believe me, the USA bumpers vs. Euro bumpers are not going to be what saves you. It will be the crumple zones in the body.
Ken300D