CPU 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.