LAST TIME we looked at the plain vanilla AMD Radeon HD6870 graphics card holding its own against the super overclocked Nvidia Geforce GTX460 from Gainward. This time, we'll see how a pair of those HD6870 cards scale up in Crossfire and hold their own against the Green Goblin's GTX580.
Nvidia's GTX580 is the new king of the single-GPU block until the HD6970 appears in another month or so, even accounting for its freshly rumoured delays. The comparison is also interesting because a pair of HD6870s sell for quite close in actual retail price to a single high-end GTX580, in particular the $550-class overclocked varieties by Asus, Gainward and others.
Since I tested the GTX580 on higher end systems, I set up another fast configuration to review the HD6870 Crossfire pair for a more of apples to apples comparison. I used the Xeon version of Intel Core i7 980X six-core extreme CPU - also known as the Xeon X3680 - together with an Asus Sabertooth X58 high-end mainboard based on MIL-spec grade components. Twelve gigabytes of memory made up of three 4GB A-Data DDR3-1600 high density DIMMs, an 160GB Intel SSD, as well as a Xigmatek 700W PSU completed the setup. Ah yes, there was also the new Xigmatek Aegir 6-pipe heat sink fan assembly, keeping the CPU around 37C at idle, or just 4C above Singapore room temperature. More about these in a separate Sabertooth review.
As you can see here, the two graphics cards fit just nicely into two x16 PCIe graphics slots on the mainboard. Unlike some other high end X58 mainboards, the Sabertooth has no extra PCIe bridges or even x8 - x16 switches, so the latency to PCIe is not affected by any such extra circuitry. Therefore, this should lead to theoretical best scaling measurements, even though the differences aren't large.
We ran the latest Catalyst 10.10 drivers on the usual Windows 7 64-bit operating system, with both 3Dmark Vantage for DX10 and Unigine Heaven 2.1 for DX11.
Here are the results for the single HD6870:
... and for the dual HD6870 Crossfire setup:
As you can see, in both performance and extreme modes, there's quite decent scaling when adding the second card, in fact even better in the Full HD-class Extreme setting with nearly double the score. With that performance, the card pair does perform better than a single GTX580 in 3Dmark Vantage by some margin. On the comparative GTX580 setups, the 3Dmark Vantage results hover around the 24,000 mark in Performance mode and 13,000 in Extreme mode, but taking into account the PhysX offload on CPU benchmarks as well.
Heaven single (top) and dual-card (bottom) results:
However, Unigine Heaven, even in this most recent update, still shows basically no speedup from a dual GPU card setup of any kind.
In summary, while awaiting the HD6970 and HD6990 - which should hand the single GPU performance crown back to AMD - Radeon afficionados can get some pretty decent performance for a few bucks by pairing up two HD6870's in Crossfire. The scaling is good, the cards are reasonably low power - two of them together cost just a bit more than a single GTX580 - and you can have a plenty of display output options with Eyefinity.
In the meantime, AMD's rescheduling of its HD6900 series announcement will hopefully result in a bit higher clock speed for the new cards, just in case they need to keep some distance from the newly resurgent Nvidia. µ