physx is your problem. turn it off or set it to low. If you want it on high you need a dedicated physx card which needs to be Nvidia. Nvidia has restricted physx so it can only be processed on their cards or a CPU. Processing on CPU is extremely slow (which is what is happening to you). You wont notice much visual diff by turning it off, just a bit less smoke and less particle effects. better than having 5 fps.