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The overclocked values are slightly better for two Radeon HD 4870 in CrossFire mode. At a resolution of 1920x1200 pixels with anti-aliasing, the MSI overclock results in an 18.6% performance increase in Crysis (where a single MSI HD 4870 OC card is 13%). If you consider all games in the benchmark suite together, the 3D performance over the standard card increases by 3.8% (a single MSI HD 4870 OC card is 3.5%).
Paired in CrossFire mode, the cards are no longer quiet. The noise level on the Windows desktop rises from 41.8 to 42.4 dB(A), but the higher fan speed drops the temperature to 63 degrees Celsius. In 3D mode, temperatures drop by 10 degrees compared to a single card. However, the noise level at 54.5 dB(A) is extremely loud, at roughly the same level as Nvidia’s GTX 260 or GTX 280.
The entire system in 2D mode consumes 242 watts, while in 3D mode this leaps to 460 watts. Anyone who wishes to use a HD 4870 in CrossFire will need a reliable power supply with somewhere between 380 and 420 watts and 32 to 35 A on the 12 volt rail.
In terms of performance, the HD 4870 CrossFire competes against the GeForce GTX 260 at 1680x1050 pixels with anti-aliasing. Backed by a more powerful CPU, we’d expect 3D performance to increase by a fair amount. The Core 2 used here means that the overall results—namely, a gain of 3.8% at double the price for two cards—is of less interest.
If you use the single card with the default clocking rate as the basis, the overclocked MSI models only show a 7% to 10% increase. If you look at the resolutions separately, the increase gained by CrossFire at 1920x1200 pixels with anti-aliasing is nearly 20%. At 1680x1050 pixels with AA, it is 18%. And at 1280x1024 pixels with AA, the gain is limited to around 6%.
These values are not unexpected. Only the new CPU classes are able to free up more performance with two cards. Older CrossFire combinations like the HD 3650, running current games and matched up with our CPU, are now able to achieve an increase in overall performance of over 60%. If you look at some of the games and resolutions carefully, CrossFire can be worth spending extra money on today. Mass Effect at 1920x1200 and 4xAA with the HD 4870 runs at 38.6 fps, but with the HD 4870 CrossFire it hits 74.0 fps. World in Conflict at 1920x1200 and 4xAA with the HD 4870 achieves 34.8 fps, yet with HD 4870 CrossFire reaches 44.6 fps.