The Lightroom Help team put together a “Performance Hints” tech note to help troubleshoot and aid customers with performance issues.
Very useful information. I have noticed that using a Wacom pen for editing (I have avoided crossing into PS) creates very large catalog entries, and that after an hour of working through a shoot making changes the RAM tally creeps up rapidly, simply restarting LR returns this but my catalog stays large. Most photographers I know are trying to minimize their PS edits where the bulk of the work can be done in LR, however this memory leaking needs to be something addressed in LR5 or somehow recovered when moving to the next image; I love LR but the response “throw a bigger spec at it” is a brutal way to improve a product.
Moving LR, its catalogs and caches onto an SSD does not give a large speed boost (not if the images are on an HDD), but it certainly makes it snappier and catalog optimization & backup are a lot better. However the biggest speed killer for me is any .psd created after external editing which can be massive and can make LR quite jumpy unless I flatten the image first.