As you've not ordered it yet Dr Who CHANGE THE MOBO
... the DFI Crossfire board is over priced, underspecced and well if the ultimate OCuK build uses the Asus, so should you /wink.
There have been people with issues with the Asus but they seem to be centered around the CPU's who's voltage demands are high and thus you can't overvolt them too well however I believe the FX is low voltage so no problem and certainly the ocuk build is awsome and overclocked with the Asus board.
Oh and it wouldn't surprise me if Quad 7800's where beaten but dual X1900's