Anandtech published a review of Intel's six-core Dunnington, you can check it out over here.
The Xeon 74xx, formerly known as Dunnington, is indeed a very interesting upgrade path for the older quad socket platform. All Xeon 74xx use the same mPGA604 socket as previous Xeons and are electrically compatible with the Xeon 73xx series. The Xeon 73xx , also known as Tigerton, was basically the quad-core version of the Xeon 53xx (Clovertown) that launched at the end 2006. The new hex-core Dunnington combines six of the latest 45nm Xeon Penryn cores on a single die. As you may remember from our dual socket 45nm Xeon 54xx review, the 45nm Penryn core is about 10% to 20% faster than its older 65nm brother (Merom). There is more: an enormous 12MB to 16MB L3 cache ensures that those six cores access high latency main memory a lot less. This huge L3 also reduces the amount of "cache syncing" traffic between the CPUs, an important bottleneck for the current Intel server platforms.