The top graphs here are from two separate Radeon runs (colored red) while the green results are for the two NVIDIA runs. See the two dotted lines running across the plot at 16.7ms and 33.3ms? This denotes how much time the GPU spends at or above 60 FPS (16.7ms per frame) and 30 FPS (33.3ms per frame). The Radeon cards only break the 30 FPS mark a handful of times. The 1% latency, meaning the worst 1% of all results, is 27ms for the Radeon cards, or 37 FPS.
The NVIDIA results, on the other hand, are quite different. The GTX 770 broaches the 30 FPS barrier many times in the same seven minutes, with a 1% frame time of 36.9ms, which works out to 27 FPS. This difference is apparent when you play the game; the NVIDIA cards seem to hitch and stutter randomly. It's not terrible, but it's definitely noticeable when racing through the disintegrating streets of Shanghai. The gap in 1% frame time results (27 FPS for the GeForce vs 37 FPS for the Radeon) is a much better indicator of the relative difference between playing with the two solutions.