Are you sure you don't mean the Ultra-D? I could've sworn DFI only had one SLI board, the SLI-DR, and the Ultra-D was single PCI-E. Although the Ultra-D you can mod pretty easily into a 16x/2x SLI board if you wanted to.
They are both about the same, if you wanted to save some money I'd buy the Ultra and just mod it, but as far as performance goes the 8x/8x has its up and downs and the 16x/2x has its ups and downs.
Intel C2D E6320 / AMD Athlon X2 3800+
Gigabyte 965P DS3 / DFI nF4 Ultra-D
2GB OCZ Gold PC2-6400 / 2GB OCZ Gold PC4000
eVGA 8800GTS 320MB / eVGA 6800GS 256MB
150GB Raptor / 74GB Raptor
2x500GB / 320GB
OCZ GameXStreme 850w / OCZ StealthXStream 600w