Setting Physx Config

So currently I an Nvidia 550 ti, which was an upgrade from my older Nvidia Geforce 250.  I am wondering if i can get any noticable perfomance improvement if i pair the 550 and 250 together as the 250 becoming a dedicated Physx processor.  I am wondering if this is possible or if it is even worth doing.  I currently have a board that only supports crossfire but i am going to eventually get an SLi supporting board on my new haswell build.

Dedicated Physx is pointless. No real improvement.