It may actually be your graphics cards. Some motherboards can leverage the GPU to boost overall performance by offloading from the CPU to the GPU the process threads better suited to a GPU's instruction set.
Seeing as you now have two of the same graphics cards working in tandem, it does not surprise me your computer is running faster.
Seeing as you now have two of the same graphics cards working in tandem, it does not surprise me your computer is running faster.