Same issue here. LR 5.3 was running fast as can be and now 5.4 is extremely slow to import and render files (Canon, Nikon, Leica and Fuji). New Catalog for each event, catalogs on external drives running fine. Pretty unacceptable when trying to import 4,000 images.
Can't firgure out how to revert back to 5.3 though. Any advice? I've tried uninstalling 5.4 but every time I reinstall Adobe makes me update to 5.4 again.
imac 27" 2.9ghz OSX 10.8.5
