Adobe have released a lengthy document on optimising system performance for Lightroom.

For best results, take a holistic approach. Read all of the suggestions here. Consider which ones to implement within the context of your computer setup, the types of files you use, and your particular workflow. Each circumstance is unique and requires a different combination of techniques to achieve the most efficient performance from Lightroom.

Good to have all this info in one place, and from the horse’s mouth.

For me the big word they use is “holistic”. Translation: Lightroom puts a lot of demands on most aspects of your system, and if there is a bottleneck Lightroom will expose it.