PCI pass-through of NIC to PV DomU... worth it?

[David Howland <metalliqaz%fastmail.fm@localhost>]

Either my Google-fu is weak or nobody has actually asked this in the 
open before...

Is it worth it to try and use PCI pass-through to give a NIC to a PV 
DomU?  I'm setting up a DomU firewall/router.  I want the latency to be 
as low as possible.

I need to know which is faster: the PV network interface or passing the 
NIC?  I don't have VT-d support, but the server is a dual quad-core Xeon 
setup, so I shouldn't be short on compute cycles.  My gut is telling me 
that there wouldn't be any tangible difference, but I want to hear what 
the experts think.

Thanks for any insights.

-d