Another month, another world-beating CPU from Intel . In April, Intel launched the Core 2 Extreme QX6800. This week, it's taken the wraps off its latest quad-core killer, the monstrous Core 2 Extreme QX6850.

As the minor modification to the moniker indicates, this latest chip is a modest overhaul rather than an all-new CPU. It remains based on Intel's 65nm production process and only ups the ante in terms of headline clockspeed from 2.93GHz to an even 3GHz.

Put another way, that's an enormously underwhelming 2 per cent boost in the headline operating frequency. More noteworthy, however, is the introduction of a significantly faster CPU bus. Previous performance variants of the Core 2 family sported 1,066MHz buses. With the QX6850, Intel has introduced its first 1,333MHz-bus processor for the desktop.

The QX6850: just one of the family

In fact, the QX6850 is just one member of a whole family of new 1,333MHz-equipped processors being launched. A further four models, all more affordable dual-core chips, join the QX6850 at launch. UK retail prices will range from around £100 for the entry level 2.33GHz E6540 to approximately £600 for the flagship QX6850. Taking up the midrange slack are the E6750 and E6850 chips, yours for £140 and £175.

Intriguingly, these prices are actually less than the equivalently-clocked 1,066MHz processors that remain in Intel's price lists for the time being.

If that seems odd, the explanation is simple. Only Intel's latest P35 and X38 motherboard chipsets officially support the new processors. By pricing them below the older, theoretically inferior 1,066MHz CPUs, Intel is clearly trying to encourage system builders to buy into its latest platforms.

All else being equal, therefore, just how much impact does the 30 per cent faster bus have on overall performance? For starters, it's worth noting that it won't make a great deal of difference to the dual-core members of the Core 2 family. Thanks to the snazzy shared cache memory architecture of those chips, bus bandwidth is not hugely critical.

Quad-core conundrum

But it's a different story for Intel's quad-core processors. In fact, Intel's quad-core CPUs to date have been little more than a pair of dual-core processor dies crammed together onto a single CPU package.

And that's important, because it means that any sharing of data or communication between the two dies must travel via the CPU bus. In other words, a journey to the motherboard and back via the Northbridge chip is necessary.

Needless to say, that's a slower, laggier process than the core-to-core communications that take place on a fully integrated multi-core die. On paper, therefore, Intel's quads are much more sensitive to bus speeds and bandwidth.

But not, it seems, in reality. In our comparison benchmarks, the new QX6850 delivered low single digit performance increases, in percentage terms. Whether it's gaming and media encoding or 3D rendering and synthetic performance tests, Intel's latest is only marginally faster than the previous incumbent, the QX6800.

Of course, it's still the fastest PC processor on the planet. It just doesn't represent much of an immediate performance upgrade.

Indeed, we've a feeling that Intel is sandbagging with this latest processor. A quick overclocking investigation revealed a chip apparently happy to run at 3.5GHz. That's a healthy improvement over the QX6800 which, as Dell has proved , typically wasn't terribly happy running much above its stock 2.93GHz frequency.

Where for art thou AMD?

All of which only emphasises that AMD desperately needs to wheel out its upcoming quad-core Phenom processor . As our benchmarks show, the fastest current dual-core AMD Athlon 64 X2 processor is way, way off the pace.

As for chipset support for the new Intel 1,333MHz processors, the aforementioned P35 item is the only official option currently available from Intel. However, boards powered by Nvidia's 680i chipsets will also support the new bus speed courtesy of a BIOS upgrade.

What's more, several board makers have been shipping premium models based on the older Intel 965 chipset that will also provide support, again via a BIOS upgrade. Owners of existing 965-equipped motherboards should refer to their manufacturer's website for more information.

Benchmarks

PCMark05 CPU performance
QX6850 9576
QX6800 9345
AMD 6000 6157

Cinebench 9.5
QX6850 14s
QX6800 14s
AMD 6000 26s

3DMark 06 CPU Performance
QX6850 4668
QX6800 4435
AMD 6000 2183

Windows Media Encoder
QX6850 1m 34s
QX6800 1m 31s
AMD 6000 2m 53s

Quake 4
QX6850 151fps
QX6800 148fps
AMD 6000 128fps

Also see: Intel launches Core 2 Extreme mobile processor .