I've been looking at video cards that have the crossfire technology, but some of them say GDDR5. My PC uses DDR3 memory. Is GDDR5 a new type of memory? Sorry, I know nothing of graphics cards. As long as I had enough additional memory to support the amount of memory required by two crossfire graphics cards, would GDDR5 be compatible with my mobo? I have 4GB of DDR3 now, but can upgrade to 16GB. (Specs below for compatibility issues). Thanks!