OWC replaced the stock Xeon 3.6GHz 6-core processor with Xeon E5-2667 Version 2 8-core processor clocking in at 3.3GHz. It worked, and the testing proved that the replacement CPU provided a performance increase of 30% over the stock processor that Apple had installed. Currently, Apple is only offering 3 different processor configurations with one 6-core, 8-core, and 12-core options.
The fact that users are able to select another CPU option that is more powerful is great, but because of the cost of Intel Xeon processors it will not come cheap.