To be honest, the slowest preset doesn't do sh** in terms of quality. I tested it on my i7 5820k @ 4.4 Ghz. I could do 720p@30 FPS at the slowest preset as long as I locked the framerate, and the difference between the medium and slower preset isn't visible at all, so it's not worth it. I found out that presets aren't effective at all unless you stream at a high bitrate, fps, resolution or all of these three combined. Actually...don't focus on the presets at all. Veryfast is good enough, slower presets barely do anything.