I can't speak to win 8.1, however LR CC had some similar issues with my win64 machine, i7 3.2 ghz, 32GB ram machine. I moved the catalog off of C, where it has always been with previous versions and the difference was amazing.
CPU usage for my machine will hit close to 50% to 70% briefly, but when I am just working in an image, with the sliders, etc, it tends to be at 25% and then only briefly.
You might try moving the catalog and or a total reinstall of LR CC.
Paul