neither, IMO. looks like they would work out pretty well. But to be sure, let me look a little closer.
EDIT: the Q9400 is a fairly high end Quad sporting the 6Mb cache/1333Mhz FSB/45nm and the Asus P5Q3 is a great board as far as support for the Yorkfields as well as PCI-E 2.0 (5G/T's) and other good stuff like DDR3 RAM. It looks good to go except as Rohan mentioned - The case. I tend to use larger cases. But through experimenting, I like mid tower ATX cases with the PSU on the bottom. I would suggest a CM690 or an NZXT Tempest. But I'm not sure if Ibuypower sells them...
EDIT: They sell both on the build you want. Up to you for looks and performance. I really like the CM690 for the rear-mount socket cooler.
EDIT2: Where in the hell did I get ATX 2.2 from :F I meant standard ATX specification. ATX 2.2 is along the lines of 12v rails >.>