Intel Core 2 Extreme QX9-series

Verdict: The worlds fastest and most overclockable CPUs.

The Core 2 Extreme QX9650 was the world's first 45nm CPU, a massive (or should that be miniscule?) step forward in manufacturing technology that means this CPU runs cooler, uses less power and can run at a higher frequency than its 65nm forebears.

Intel also tweaked the Core architecture inside the QX9650. The end result, called the Penryn architecture, features an improved radix divider known as radix-16, which can calculate two bits per iteration, and a Super Shuffle Engine that improves the performance of SSE instructions. The Penryn architecture also introduced SSE4, which adds a further 47 instructions to the x86 set, and the new CPUs have more Level 2 cache than their predecessors - 6MB per pair of cores compared with 4MB in the Core 2 Extreme QX6-series. As the Penryn architecture is based on the Core architecture, it also supports 64-bit instructions, SpeedStep, Execute Disable and SSE3. The QX9650 has a fully unlocked multiplier, so it's very overclockable.

The four cores of the Penryn-based QX9650 run at 3GHz and share a 1,333MHz effective FSB, the same frequency as the QX6850. However, as a result of the architectural improvements and enlarged Level 2 cache, the QX9650 performs better than the QX6850 - 11 per cent faster in our Media Benchmarks, 10 per cent faster in Cinebench R10, 7 per cent faster in Folding@home and 19 per cent faster in Crysis. The QX9650 also consumes 44W less power than the QX6850 and is more overclockable, as it's easily overclocked to above 4GHz with a standard HSF.

Intel plans to launch a higher-spec Penryn architecture CPU in January called the QX9770. The QX9770 runs at a higher 3.2GHz frequency than the QX9650, and has a faster FSB (1,600MHz effective). Partnered with a suitable motherboard chipset, such as the Intel X48, it provides much more memory bandwidth. As a result, the QX9770 is the fastest single-socket CPU in the world - it's a stunning 77 per cent faster than the fastest AMD CPU, the Phenom 9600.

Both Core 2 Extreme QX9-series CPUs are astronomically expensive but, thanks to their Penryn architecture and 45nm transistors, they're incredibly fast and overclockable. They also provide a great sneak preview of what the Penryn architecture non-Extreme edition Core 2 Duo and Quads will look like early next year.