DiRT2 at 2560 x 1600
As soon as we move up to 2560 x 1600 the HD 5800 series of models come into play as we can clearly see the HD 5700 struggles at this high resolution on the high preset. While there's little difference between the minimum of the two HD 5800 series cards, we can see that the HD 5870 does pull in a much higher average that equates to about a 20% increase.
Cranking the preset to Ultra we can see it's all down to the HD 5800 series of cards with the HD 5850 managing to come in a good 20% above the 30 FPS minimum we want to see when we're setup like this.
As we move up in the video card power department though we can see the HD 5870 and HD 5970 really move away from that 30 FPS minimum giving us an absolute load of breathing room.