CPUOver at World's keen eyes spotted that Intel has quietly been shipping a Xeon X5698 with a frequency of 4.4GHz:

In the middle of last year, when Intel produced pre-production parts for the next refresh of Xeon 5600-series, they also made several quite interesting Xeon samples. The most distinguishing feature of these chips was very high clock frequency. Even the slowest Xeon microprocessor from that group was clocked at 4 GHz, and the fastest one reached 4.66 GHz. One of these samples made into production, and started shipping earlier this year. The processor was released as Xeon X5698, and, at 4.4 GHz, it's the fastest Intel production CPU ever.

Intel Xeon X5698 is built on Westemere microarchitecture, and, with a couple of notable differences, shares many features with other Xeon 5600 chips. One of the differences, extremely high core frequency, we already mentioned above. This model has only two active CPU cores, and we believe that 4 other cores on the die are disabled. The processor comes with 12 MB L3 cache, HyperThreading, and works in socket 1366 motherboards. Intel X5698 has OEM part number AT80614007314AA, and S-spec number SLC32. We suspect that this SKU will be shipped only in OEM systems.

For the sake of history, we included information on all "special" Xeon samples, produced in 2010, in the table below: