Pentium® Extreme Edition

The Pentium Extreme Edition was introduced on May 1st 2005 as the new flagship of the Intel desktop range, approximately three weeks before the Pentium D. Both generations of the Pentium Extreme Edition followed the same formula, take the current Pentium D core and enable the hyper-threading. The later Presler based chips also added in a faster 1066MHz (4 x 266) front side bus.
The Pentium Extreme Edition also got unlocked multipliers, both up and down from the default, where as all other Intel processors had this locked. This gave extra flexibility to overclockers to extract the maximum performance from there PC.

For the 90nm Smithfield the addition of hyper-threading was a mixed blessing, in applications that could genuinely make use of 4 threads it could offer some quite significant gains, but in some cases it instead hindered performance. Ironically the place where the flagship gaming CPU really excelled was in media encoding while some games would perform better with hyper-threading disabled in the BIOS.

The Presler based Extreme Edition 955 came out on January 16th, 2006, and the hyper-threading could still hurt performance compared to if it was disabled, but the increased front side bus generally meant that even with it enabled it could still outperform the Pentium D 950. Due to the increased bus speed it also had a slightly increased clock speed, 3.46GHz vs. 3.4GHz for the D.
On March 22nd the 965 was launched which saw the clock speed bumped to 3.73GHz and remains the highest clocked dual core processor so far.

Pentium® Extreme Edition 840

Live system pull, currently unused but fully working.

Pentium® Extreme Edition 955

Live system pull, currently used in my media centre system.