I just bought an HIS 4890 1GB graphics card. My old card is a Powercolor HD2600 XT 512MB GDDR3. I've read that crossfireX allows two different models of graphics cards to work together. I have a motherboard with two PCI-e slots. Is there anyway that I can use the HD2600 XT to make my 4890 better? Or is there an ATI version of PhysX?