Intel has given its family of three Core i7 processors an overhaul and has replaced the high-end Core i7 965 Extreme with the Core i7 975 Extreme. The change is fairly minor and raises the clock speed from 3.2GHz to 3.33GHz. Intel has achieved this increase by raising the 133MHz base clock multiplier by one notch from 24x to 25x.

The higher clock speed results in a performance increase of four percent across the board compared to the Core i7 965 Extreme, as the other features in the Core i7 975 Extreme have been carried across from the previous model.

The power draw of Core i7 975 is 5W higher than the 965 when idling in the Windows desktop at standard speed. We could easily overclock the Core i7 965 to 3.87GHz on an Asus P6T SE motherboard with 3 x 1GB Kingston DDR3-2000 RAM running Windows Vista Ultimate Edition, while the Core i7 975 would hit a nice round figure of 4.0GHz.

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At these overclocked speeds the Core i7 975 drew 10W more than the Core i7 965 when the system was under load, and we are pretty sure that any motherboard that supports current Core i7 processors should have no trouble with the new model.

It is interesting to note that Intel has not simply added the Core i7 975 at the top of the existing range of Core i7 processors but has instead replaced the 965 with the 975. The chip giant has also replaced the 2.93GHz Core i7 940 with a new 3.06GHz Core i7 950, however the 2.66GHz Core i7 920 remains in place at the bottom of the range.

We regularly find that Core i7 920 will overclock to 3.9GHz, which is the same speed we get from a Core i7 940 or 965 Extreme. In other words the overclocking enthusiast can happily buy a relatively cheap £240 Core i7 920 and achieve the same results they would get with a £770 Core i7 965.

The new Core i7 975 will overclock to 4.0GHz and therefore has a tiny margin of performance over Core i7 920, but you have to wonder how many people will pay £800 for the privilege of an extra 133MHz.

Intel has created the new 975 Extreme with a revision to the original Core i7 that takes the silicon from version C0 to version D0. The intriguing thing is that Core i7 920 has also been updated to version D0 and while our new 920 would not overclock any further than the original version, it is considerably more efficient.

At the standard speed of 2.66GHz speed the D0 draws 15W less power than the C0 and, when we overclocked to 3.9GHz, the difference in power draw increased to a hefty 55W in favour of the D0.

We cannot recommend the Core i7 975 Extreme due to its ridiculous price, but the new version D0 silicon is a definite improvement over C0. Happily there are alternatives to the 975 Extreme and we are very impressed by the new version of Core i7 920.