Amos Lee from Gigabyte just let us know about their new series of 667MHz FSB Pentium 4 supported motherboards, which include 7 in total. As thought by many and for obvious reasons, Intel have gone with a 667MHz FSB specification instead of a 666MHz specification (166.66 x 4 = 666.64) and rounded it up (just like the Celeron 667MHz processor days) - That would be the likely reason given anyway, we think.
The P4 Titan 667 series was designed to meet and qualify for next generation CPU specification, from current FSB 533MHz reaching up to FSB 667MHz. Predicting from the past Intel® Pentium® 4 Processor evolution history, the new system bus frequency might increase from the currently 533MHz up to 667MHz. The new FSB 667MHz specification greatly increases the bandwidth between the north-bridge chipset and CPU from current 4.2GB/s to 5.3GB/s. This is accomplished through a physical signaling scheme of quad pumping the data transfers over a 166-MHz clocked system bus and a buffering scheme allowing for sustained 667-MHz data transfers.More information in our New Products Forum