I have been researching Crossfire configurations. X1900 XT crossfire comes configured with another X1900 XT. Is the same configuration available using X900 XTX cards? Does the X1900 XTX come as a slave/master setup as does the X1900 XT? Any suggestions as to the best configuration? What would be the performance difference. My motherboard supports X1900 XT crossfire. Thanks for reading and any suggestions.