Thank you very much for your thorough, helpful answer! 
I'm staying with tried and true Sandy Bridge for now: Q67 + i5 2500. Mostly because finding a micro-ATX motherboard with VT-d (for certain) isn't easy. I found the Intel DQ67SW and the Gigabyte GA-Q67M-D2H-B3, as they clearly state the feature as present in their specs page or the manual.
Do you know if the GTX 680 works via IOMMU in Xen? Same question for the 580?
Edited by Roman2K - 4/14/12 at 5:47pm
I'm staying with tried and true Sandy Bridge for now: Q67 + i5 2500. Mostly because finding a micro-ATX motherboard with VT-d (for certain) isn't easy. I found the Intel DQ67SW and the Gigabyte GA-Q67M-D2H-B3, as they clearly state the feature as present in their specs page or the manual.
Do you know if the GTX 680 works via IOMMU in Xen? Same question for the 580?
Edited by Roman2K - 4/14/12 at 5:47pm















. Plus, Xen is part of the mainline kernel