Just how much are you willing to pay to have the fastest graphics card? That's always been a tricky question for PC gaming enthusiasts.

But with the release of ATI's latest performance graphics chipset, the Radeon HD 4870, it's become a real conundrum.

That's because AMD's graphics subsidiary has given up chasing the outright 3D performance crown.

It is no longer even trying to create the fastest single GPU on the planet. Instead it has shifted its focus towards efficiency and value for money.

As we discovered last week with our first look at the entry level member of the Radeon HD 4800 series, the 4850, ATI has done a stunning job. The 4850 is yours for a piffling £125 but delivers more performance than the fastest single-GPU graphics card available just a few months ago.

Say hello to the 4870

As good as the 4850 is, however, the new 4870 variant is even more impressive. Yes, it costs 50 per cent more than the 4850 but doesn't quite deliver 50 per cent more performance. The 4850 still offers the best 3D bang for buck.

But the 4870 has an even better party trick. It makes the latest uber-GPU from arch rival NVIDIA, the GeForce GTX 280, look massively overpriced and just a little bit silly.

You can find full technical details of the silicon gubbins that lie at the heart of the 4870 in our original Radeon HD 4800 series review. But to recap briefly, the really clever bit is how ATI has managed to up the shader and texture count by 150 per cent courtesy of a boost in transistors of just 40 per cent.

In many respects, the 4870 is no different from the cheaper 4850. It has the same 800 shaders, 40 texture samplers and 16 render output units.

Likewise, it sports an identical DirectX 10.1 feature set (something NVIDIA cannot yet match, for better or worse) and the same 256-bit memory bus and 512MB frame buffer. But that's no surprise. After all, both are based on the RV770 GPU.

Cranking up the clocks

The 4870, therefore, is all about clockspeeds. In terms of core frequencies, it ups the ante by 125MHz to 750MHz. However, the big news is memory clocks.

The 4850's GDDR3 memory trundles along at a relatively pedestrian 2GHz. But ATI has bolted the very latest 3.6GHz GDDR5 chips to the 4870.

That's an extremely important upgrade because NVIDIA's beastly GeForce GTX 280 has the advantage of a much wider 512-bit memory bus. Factor in the GTX's 2.2GHz GDDR3 frequency and it retains a raw bandwidth advantage. But it's nothing like as big as it would have been had ATI stuck with GDDR3 for the 4870.

The only other significant difference is a change in form factor and power consumption. The 4870 is a dual-slot board that requires two six-pin power cables where the 4850 is a single slotter that can survive with a single power cable.

Anywho, you can read all about the GTX 280's architectural nitty gritty in our review. What you really need to know is just how close the 4870 gets to NVIDIA's finest. And remember, prices for the 4870 kick off at just under £200. You'll do well to get any change out of £400 for a GTX.

What about the benchies?

Our first performance test is the 3D technofest that is Crytek's Crysis. It's both the most advanced and most graphically demanding PC game yet. With all the image quality options set to full reheat, it will bring any video board to its knees.

The Radeon HD 4870 is no different in that regard. But crucially it makes almost as good as fist of coping with this particular graphics Crysis as the NVIDIA GTX 280.