Battlefield 3
We tested Battlefield 3 by playing through the start of the Kaffarov mission, right after the player lands. Our 90-second runs involved walking through the woods and getting into a firefight with a group of hostiles, who fired and lobbed grenades at us.

The game was run at its highest detail preset, Ultra, which couples MSAA and FXAA antialiasing as well as snazzy DX11 effects and tessellation.

Things get a little strange here. The 7870 Black continues to do well, but the 7850 Black actually falls slightly behind the reference 7850. The difference amounts to less than half a frame per second, so for all intents and purposes, we can say the two cards perform identically. But that doesn't make sense—the Black Edition is clocked 115MHz above the reference card, and its memory is 50MHz faster.

We re-tested, tweaked PowerTune settings, checked for overheating, and poked and prodded trying to find the source of the problem, but nothing seemed out of order. We even tried clocking the XFX card at the same speeds as the vanilla 7850, and performance declined further. Suspecting a memory latency difference, we called XFX for comment. The company said that, save for clock speeds, the Black and reference cards should be identical at the firmware level. Any straightforward explanations for the performance discrepancy were suddenly ruled out.

Later that day, the company got back to us again. They'd spoken to another reviewer, and guess what? The 7850 Black's higher-than-normal clock speeds didn't seem to "do anything" in some cases, he said.

In other words, we may be looking at a bizarre, presently unresolved bug with this particular card. Maybe the bug lies in the drivers, or maybe it's some hidden firmware kink. The question is, does it rear its head in other games?