q264 Speed on has1
(Click thumbnails to open the full-size images.)
These show the frames per second (FPS) of q264 at each H.264 profile on the Haswell system. Generally high quality means lower speed. Unlike previous generations, this generation of Quick Sync shows good differentiation between the different speed-quality settings.
q264 Quality on has1
These show the PSNR metrics of q264 at each H.264 profile. Excluding the highest speed (7), there is very little difference between the quality of the encoding at the different speed-quality settings.
Given these results and the FPS results above, there is probably no reason to ever use speed-quality setting 7 because it is a significant drop in quality for a relatively insignificant increase in speed. Further, there is very little benefit to using a quality setting beyond (lower than) 4, because the higher quality settings slow down the encode with little or no increase in quality. And in fact there's an argument to be made that speed-quality level 6 (the second fastest) is a good trade-off if you care about speed at all, because it doesn't sacrifice much quality.