Saying more good things about Dunnington ( Intel Xeon 7400 ) feels a bit like piling on. There are a myriad of posts out there about how great Dunnington is. If you are looking for some data to support enterprise selection of the 7400, the article in Anand Tech Intel Xeon 7460: Six Cores to Bulldoze Opteron is very compelling. One of the exciting parts of this article is in the section on ESX performance, especially with vm's configured with multiple "virtual cpu's". This is a configuration some of my large enterprise customers seem married to - even when not needed... The 7400's use of highly efficient 45nm penryn cores delivers the dominant performance for this usage model. There is a lot more to this processor than "2 more cores".
To quote from the article "This 45nm Intel core features slightly improved integer performance but also significantly improved "VM to Hypervisor" switching time. On top of that, synchronization between CPUs is a lot faster in the X74xx series thanks to the large inclusive L3 cache that acts as filter. Memory latency is probably great too, as the VMs are probably running entirely in the L2 and L3 caches. That is the most likely reason why we see the X7460 outperform all other CPUs."
The ESX section concludes with "Xeon X7460 is again the winner here: it can consolidate more servers at a given performance point than the rest of the pack"
Xeon 7400 is the processor for virtualization.