One thing that has always bothered me is that in the transition from an 11 year old notebook to a mid-to-high level PC, playback and especially reverse playback always suffered from the same lags and framerate drops. There wasn't the improvement I expected. In the Preferences > Performance tab, I tried increasing the "Cache size" from 256MB (default) to 4096MB without noticing any change (I have 32GB of RAM). I never touched the "Seconds to preroll renders" option, which by default is 0.5 seconds. Now I've tried to set it to 1.0s and the improvement in playback and reverse playback is EVIDENT! If anyone feels like trying to take a problematic project in timeline and increase the preroll time and then report the results, it would be a favor to me. If the improvement is also confirmed by others I will immediately put the tip in the manual, because it seems very important to me.