I think it might be pretty hard to compare, really. I mean there's a lot of variants such as memory link architecture, length of traces between individual processors vs being built-in, and also how much bandwidth is available per core or processor.
I don't think anyone can really answer that until the dual-core systems are finalized, analyzed, and reviewed thoroughly. Not to forget, also build a dual physical CPU system that might be relatively close. How would a P4 EE stack against a Xeon? Itanium 64?