MacPro: Which Xeon to Choose for Upgrading

Many users have contacted us concerning the model of Xeon CPU installed in the MacPro in order to perform a CPU upgrade.
One should be cautious about Xeon, because in the past Intel has been releasing numerous Xeon processors, and there are almost as much Xeon chipsets.
The MacPro is powered by 2 Intel Xeon "WoodCrest", identified by a serial number 51xx. The low-end MacPro is equipped with a Xeon 5130 (2.0GHz), while the default model is sporting a Xeon 5150 (2.66GHz) and the high-end MacPro has 2 Xeon 5160 (3.0GHz). The price per CPU varies from 400 to 950 Euros.
One can find on the market, Xeon named 50xx, much cheaper and with a higher clock frequency, such as a 3.7GHz model for 900 Euros. But such Xeon are designed to be used on a 1066MHz FSB, and not the 1333MHz FSB found in the MacPro. In addition the Xeon 50xx releases much more heat than the WoodCrest while being much more power-consuming.
Upgrading the Xeon CPU of a MacPro is currently not a good deal, but it will for sure be interesting to perform such operation when Intel will release Quad-Core Xeon at the beginning of 2007.