Step 1: CrossFire With Two GPUs
One Radeon HD 6870 X2 Gives Us CrossFire With Two GPUs
Let’s revisit that PowerColor Radeon HD 6870 X2 for a moment. This card places two Barts GPUs on a single PCB and connects them through the use of a bridge chip from Lucidlogix.
The first graph gives us performance in Call of Juarez at 1920x1080 using the Radeon HD 6870 X2 board. It's easy to see that the average frame rate of the PowerColor card nearly hits two times one Radeon HD 6870 on its own. But we also see how choppy that graph is compared to the single-GPU setup rendering on its own.
While some of the peaks approach 200% of one GPU's performance, the frame rate drops dramatically in other spots, barely exceeding the speed of a single Radeon HD 6870. Gamers see the elevated average frame rate and assume a great experience, but then experience those valleys in the graph as brief (but perceptible) stuttering.
Two Radeon HD 6870s Also Give Us CrossFire With Two GPUs
Now, let's compare the behavior of the Radeon HD 6870 X2 with a pair of regular Radeon HD 6870s connected with a CrossFire bridge. That's a pair of boards totaling $360 facing off against a $470 dual-GPU card.
It turns out that the average frame rates are comparable. However, the setup without Lucidlogix's bridge chip demonstrates slightly smaller performance dips.
Despite the almost-negligible performance advantage and a more than $100 price difference, the inconsistent frame rate of two cards working cooperatively remains a potential issue for some folks.
With that said, it would only make sense to use PowerColor's card if you didn't have the four slots worth of expansion space to fit two Radeon HD 6870s. The Lucidlogix bridge's only advantage is one of convenience; it doesn't improve performance in any way.