I posted a link recently to a clothing company that makes bike gear with soft armor. The guy who runs that place make vehement arguments against hard armor. He argues it does not absorb the impact but simply spreads it around. That does not sound too bad to me. Would you rather be hit with a hammer or a hammer and a nail? Having a combination of both would seem like the best solution. Spread the force around and then absorb that lesser force.
If you are looking for a back protector (and have faith in the CE testing methodology, that guy does not), then the best one around just now is the Forcefield Pro Sub4.