I'm currently running two HD4870 cards in Crossfire, but since my board will handle quad-Crossfire I was thinking of running four HD4670 cards instead.
I like the 4670 because they're smaller and don't require any external power source. (And besides, four cards just looks cooler.) No way am I going to fit four 4870 cards in there and power them and make it look even halfway decent.
Given that the PCIe will be cut from 16x to 8x with four cards running, does anyone have any opinions on performance comparison between these two setups?