ATI Radeon HD 5770
It's only the relatively poor performance increases in Just Cause 2 that stops the low-end cards of this CrossFire test posting a more impressive average increase with a second card.
The 80 per cent and 85 per cent in Far Cry 2 at 2,560 x 1,600 and 1,680 x 1,050 respectively boasts better scaling than both NVIDIA's Fermi cards.
At £260 for a pair of HD 5770s though you're getting significantly better performance than a single HD 5850, which is practically the same price. With the improvements, by AMD's driver team especially, in multi-GPU gaming you actually are better off with twin HD 5770s than a single HD 5850.
The most surprising thing though is the fact that twin HD 5770s actually beat a single GTX 470. Impressive stuff.
ATI Radeon HD 5850
If you're rocking an existing HD 5850 then the news is good. Dropping in a second card will give you some serious performance gains, especially at the high-end resolutions.
In terms of all round speed gains the HD 5850 is the best that AMD has to offer with an average increase of just over 70 per cent at 2,560 x 1,600. That's behind the impressive increases of around 80 per cent that you get with twin Nvidia cards though, but CrossFire HD 5850s still represent a conundrum.
They're almost on par with the HD 5970, but significantly faster almost across the board compared to the GTX 480, a card that's only £30 cheaper than two of these at best.
AMD's multi-GPU strategy seems to be paying off.
AMD Radeon HD 5870
These are the cards that have been propping up the fastest gaming PCs for over half a year. Put together two HD 5870's cost almost £100 more expensive than the HD 5970, but offer much more in the way of gaming performance.
That said though we're into the realms of diminishing returns as the relatively moderate gains you pick up over the HD 5970 hardly justify the extra outlay.
The interesting thing though is that with the latest Catalyst drivers improving AMD's gaming performance so much it has propelled the HD 5870 ahead of the GTX 470 in single and, despite lower percentage performance gains, in dual-card configurations.
AMD's focus on the multi-GPU to help prop up it's high-end components means it works across the board.