One of the ways in which i feel Lightroom is slow is scrolling between picture is loupe view. With Lightroom's preview based strategy this has never made sense. So since I was taking this weekend to clean my computer, add a GPU and do a fresh windows install, i'd take a look into Lightroom performance. I saw some behavior that refines the advise to use an SSD for the catalog and previews and a HDD for your raw files.
First scrolling while in grid mode. As you would expect Lightroom is populating the grids based on the previews that are generated at import. On my machine, the SSD was being utilized between 4% and 8%, and i expect that the only way to improve the grid scrolling performance would be to lower latency of the drive, since the volume being read isn't high. I'd be curious if anyone has tested a pci-e nvme drive vs a sata drive in this regard (or better yet a RAM disk).
In Loupe view I expected to see the same behavior but noticed that it was the HDD that was showing between 60 and 90% activity while the SSD showed 0%. Moving the actual image files over to a 2nd SSD showed again that the SSD the files were on was under load and the SSD with the catalog/previews was again showing no activity. I repeated this experiment this time with smart previews and the behavior was identical. This also seems to be the behavior of full screen preview mode.
Bottom Line, The best storage mechanism for your actual image files is also an SSD. However SSDs are still expensive and getting the capacity needed to store your image collection may be cost prohibitive. So what I recommend is storing your most recent photos to the SSD while you are working on them and then move them onto the HDD.
Question for Adobe. The advice I've always read is to render previews at the size just larger than your screen resolution (e.g., 1440, for a 1080 screen). Why bother if you don't use the previews when displaying an image that is smaller than the screen. I would understand if you ignored the preview for the develop module but I don't understand why this would be the case for loupe view.
Are you talking about the Library Module or the Develop Module?