Interesting and quite helpful. Thanks.
While I have not tested the current state of the git repository, I thought I might add a few comments about testing performance in general from the perspective of a retired systems programmer. I am a fan of Cinelerra-GG and use it for burning bluray disks so I hope to be able to test the new code before long.
It will be interesting to hear your results of burning bluray disks -- especially if you have good speakers where you might be able to differentiate audio options of LPCM and tsMuxer results as I could not.
... Any settings within a given application, eg cache or pre-roll, will need to be measured in a controlled environment which means rebooting the computer to clear the file system file cache. Otherwise, any request for data that has been previously read may be satisfied from the operating systems file cache regardless of the settings in the application.
Measuring this in a controlled environment is very useful to a programmer to improve the code if possible. The problem is for a user, there is no such thing as a controlled environment and just how they "feel" is all that matters. So the best that can be done is for programmers to take advantage of the methods you outline. I do think that the "preroll" of 1.0 seconds as opposed to 0.5 seconds seems more consistent for me as a user -- it made me "feel" better!
... It goes without saying that any use of swap space will radically degrade performance unless that swap space is on a solid state drive and the swap partition is quite generous in size.
I gave up on swap space years ago -- if you have to swap, you may as well reboot.