i can tell a big diffeance ,maybe its just the 512 mb more memory but 4890 kills my 4870 3dmarks and ill post some scores later
@ both 4890 has higer clock speeds but 4870x2 is fater because of well,the x2. You can cf two different cards as long is they have the same architecture.
Ya ask THERMAL REACTOR. He has 4879's X2 CF.