Roughly 27% of all Steam gamers play at 1366x768 and we suspect many (most?) are using a GeForce GTX 660 or something relatively equivalent. Fortunately for that large chunk of the community, the GTX 660 averaged a very playable 49fps, and that is pretty impressive given every setting was maxed besides ambient occlusion, which was disabled.
It's also possible to achieve an average frame rate of over 30fps with the GTX 750 Ti or R7 260X, though frame rate lag is more noticeable than running at 60fps. Something we found interesting was how the R7 260X matched the performance of the HD 5870 despite being considerably older, the 5870 should be faster.