For this test, I shamelessly stole Scott's Borderlands 2 character and aped the gameplay session he used to benchmark the Radeon HD 7950 and GeForce GTX 660 Ti earlier this month. The session takes place at the start of the "Opportunity" level. As Scott noted, this section isn't precisely repeatable, because enemies don't always spawn in the same spots or attack in the same way. We tested five times per GPU and tried to keep to the same path through the level, however, which should help compensate for variability.
Here, too, we tested at 1440x900. All other graphics settings were maxed out except for hardware-accelerated PhysX, which isn't supported on these Radeons.
Yikes. Neither GPU does a good job of keeping frame times consistently low, as evidenced by the large number of spikes on both plots.
The 8790M does pull off much better average frame rates and 99th-percentile frame times, though. Then again, that 54.3-ms frame time works out to an 18.4 FPS frame rate, which is hardly anything to brag about.
According to our percentile graph, things start to go awry around the 95th percentile on both GPUs. So, about 5% of frames take significantly longer to render than the rest. That about tracks with what Scott measured in Borderlands 2 with Radeon HD 7950. (This time, though, we were using newer drivers supplied by AMD.)
Both GPUs spend a fair bit of time working on frames that take more than 33.3 ms or 16.7 ms to render. However, the 8790M is obviously faster and doesn't linger too long on frames that take more than 50 ms or so. Our seat-of-the-pants impression echoes this result. Borderlands 2 is responsive and very much playable on the 8790M, even if the latency spikes damage the illusion of motion to some degree, making animations appear not completely fluid.