The X2 processor has Intel in a faff.
ExtremeTech have had the dual-core offerings of both the big-boys, and are apparently calling the first round of the battle in AMD's favour:
We recently got our hands on a dual-core Opteron test kit from AMD, and decided to pit it against the Pentium 4 840 Extreme Edition we previewed recently. These are not chips aimed at exactly the same markets, but the Opteron is so architecturally similar to an Athlon 64 in that it provides a reasonable facsimile of Athlon 64 desktop performance. There are differences, of course—Athlon 64 CPUs don't have as many hypertransport links for multi-CPU systems, typically ship at faster clock speeds, and don't use registered RAM—but the core architecture is nearly identical. Rather than test it as a pure server platform, we used a uniprocessor system and a desktop graphics card to see how a dual-core desktop Athlon 64 might perform.
Thoughts? I'm sure the AMD fanboys would like to chime in, and of course Chipzilla Zelots will want to rebut... And remember, Marquis of Queensbury Rules are in effect, Lads - so keep it clean.
Of course, through all of this, what we don't have is any discussion as to the usage model. AMD have come out with server chips, because they believe dual-core will suck for games in the short-term. Intel doesn't want to cannibalise its Xeon or Itanium sales with dual-core server chips, and so that leaves them with just gamers. But, amusingly, there's no upgrade path - the top end EE will beat the new dual-core into a cocked hat when it comes to raw games performance.