Lesson one for the trainee PC performance enthusiast. Whether it's CPUs or GPUs, always go for a cut-down version of a flagship chip if you want to maximise your bang-for-buck ratio.

Enter, therefore, AMD's ATI Radeon HD 5850 graphics chipset. It's an ever-so-slightly hobbled version of the mighty Radeon HD 5870, which until very recently was the fastest GPU on planet Earth.

Available from £225, the 5850 is around £85 cheaper than your average 5870. That's a wallet-wilting 37 per cent price mark up for the premium part. Put another way, if the 5850 can get within 37 per cent of its beefier brother in terms of performance, it's onto a winner.

That will take some doing thanks to the 5870's 1,600-strong array of stream shaders. That's right, 1,600 microscopic processing units in a single chip. Mind boggling.

What's more, we're talking DirectX 11 shaders complete with support for the fancy new tessellator. For the uninitiated, the tessellator is a new hardware feature designed to conjure unprecedented geometric detail out of the very ether.

The 5870 also packs 80 texture units, 32 render outputs and ridiculously fast GDDR5 graphics. It's a bit of a beast. But there's more to the 5850's task than merely measuring up on price compared to its in-house competition. It must also take on a revitalised Nvidia.

The big news from Nvidia in 2010 is the belated release of the Fermi wonder-GPU, the basis of the new GeForce GTX 480 and 470 graphics boards. With three billion transistors, it's by far the most complex complex computer chip ever to find it's way into the PC. In GTX 480 trim it's also the fastest.

Admittedly, the stratospheric £400-plus pricing of the GTX 480 effectively takes it off the 5850's radar. But with GTX 470s creeping under the £300 mark and prices falling on Nvidia's older DX10 boards, the 5850 definitely needs to keep one eye on the green team.