Upload & Sell: Off
I was more annoyed by not being able to transfer all data between a Mac and the iPad, iPod, etc., except by using the cloud. The old wire cable should still be usable. Instead it is getting even more cloud based with every iteration and that, more than anything else, pushed me back to Windows when it was time to upgrade.
Robert, you're between a rock and hard place with the way you use Lr. On one hand you use minimal previews to get the images into Lr as quickly as possible. That's good because you are able to keep/reject your images easily and move on to the next one. I find too many need some sort of enhancement over the in-camera jpeg image before I can decide whether or not to keep it. That enhancement involves editing, which is especially slow in the Library module when we don't have a decent preview to work with, and can also be slow in the develop module if we don't have the image already partially converted from raw in the ACR cache.
On the other hand, if you told Lr to import everything and build a suitably large preview that easily fills your screen and/or allows full size zooming, then things will take ages for Lr get through it all. However, once done, it will be purr along very nicely in the Library module.
On the other other hand, having spent a long time building 1:1 previews, Lr still has to do most of it again if you make any edits in the develop module.
The ACR cache size is configurable in the Lr preferences. Make sure it is big enough to hold every image in your library and opening those images will always be quicker than if the entire raw conversion has to be done again. Admittedly, using SSDs speeds things up either way in my Mac experience but definitely do not leave the ACR cache on a hard drive.
The Lr Preview cache is not configurable except in terms of the size of each preview. The cache as a whole will keep growing as required. Now that I am using a large screen I use 1:1 previews. These too live on an SSD.
I also avoid using sidecar files but the impact they have on performance will be far less with a speedy SSD than with a HDD. Every time you do an edit the sidecar file will be updated and saved. That can really mess with the efficiency of a hard drive by putting the heads where you don't want them for the next step.
Because you are using SSDs you need to keep them trimmed if they do not already self-trim. Otherwise writing to them will slow down significantly over time as the SSD fills up.
A faster graphics card might speed up writing to the screen but it won't make a lot of difference unless you are using lots of pixels, such as with a 4k screen or any of the large screens with 2560x1440 or similar. However, it apparently makes a bigger difference in Ps because apart from being used to speed up sharpening and some other edits, it is also used for rotating, moving and zooming the image.
About the only other Lr speed enhancement I can think of at the moment is to not apply sharpening, noise reduction and other computationally intensive edits until as late as possible. So for example, adjust the brightness and colour enough to decide that an image is worth persisting with before you mess with NR and sharpening. That way, if it trashed then you haven't bogged Lr down with unnecessary processing. That processing will be repeated each and every time you open the image in the develop module, so it is even faster to make the changes in the library module if you can - and that in turn is faster if you already have the the correct preview built. If you try to zoom in too far then Lr will have to build a new preview and that will probably mean do another raw conversion.
A huge advantage of using the Library module when you have the right previews is that you can browse through the images very quickly without the need to do the raw conversion each and every time you display the image.