Results: Tomb Raider
We begin our analysis with Tomb Raider, which is probably a best-case scenario for Dual Graphics since the title is sponsored by AMD. It also happens to be a lot of fun.
At least on paper, these benchmark results tell us that Dual Graphics has a pretty profound impact on performance, above and beyond what an APU on its own or an entry-level discrete GPU manages. As AMD suggests, its Radeon HD 6670 delivers the best price/performance ratio paired up to the A10-6800K APU, offering a 100% speed-up compared to the discrete card on its own.
The boost we measure from the GDDR5-equipped cards is less impressive. But despite mixing the VLIW5 and GCN architectures, there's still a clear improvement.
Plotting frame rate over time doesn't tell us anything different, though we see that the Dual Graphics setups deliver notably-higher frame rates than an APU or discrete GPU operating alone.
Now we take frame time variance into account. You can see that Dual Graphics introduces a significant amount of latency between subsequent frames. This latency can be responsible for dropped and runt frames, which counteract the benefit of a higher frame rate.
In the video below, you get a side-by-side comparison of the A10-6800K APU (24.1 FPS average), the A10-6800K APU with a Radeon HD 6670 DDR3 card in Dual Graphics mode (43.3 FPS average), and a Radeon HD 7750 on its own (49.2 FPS average).
The half-speed video gives us dramatic demonstration of what Fraps doesn't tell us: the Dual Graphics configuration is as choppy as the A10-6800K on its own, despite a near-doubling of average frame rate. Meanwhile, the Radeon HD 7750 is perfectly smooth. This effect isn't as severe at full-speed, but it's still noticeable.
In this first title we're testing, it's quite obvious that there is a discrepancy between what you actually experience and what a benchmarking utility like Fraps suggests you should be seeing. The increase in frame time variance supports our hypothesis. Dual Graphics may increase the number of frames per second being rendered, but because they're predominantly dropped and runt frames, you're not actually seeing them during gameplay.