I just started to plan for next computer and started to wonder, so would PCI-e SSD speed up lightroom, when compared to SATA SSD transfers?
Although I'm sure the PCIe SSD is faster than a sata SSD, I think you will be just as happy with the sata SSD and save money in the process.
The SSD will improve load times. Your programs will run essentially the same.
That depends on what areas of Lightroom you want to speed up.
The disk speed doesn't help with most areas of Lightroom at all. It will not help with importing, developing or exporting. It only helps with loading the software, loading the catalog and loading previews. If you're still thinking a bout getting faster drives, then as I understand things, PCI-e is faster than SATA, but we may also be at the point where you'll never notice the difference, so whichever is cheaper is probably the best choice.
If you really want to speed up most areas of Lightroom (import, develop, export), you should get a faster CPU.