The e6600 is a very good processor for the 975 chipset. Notice in the link ASUS has put a note about using 45nm CPUs on that chipset. The original BIOS was released well before 45nm C2D/C2Q came out. A 65nm C2Q6600 would be ideal if a quad is what you are looking for. I have the e6600 runing on a 965 and it runs great. Stick with a 65nm chip on that MB and the e6600 or Q6600 are a great solution.