You could have been hit by the fact that LR can have issues with more than 4 cores.
AFAIK, Adobe is aware of this and is working on an improvement. If you think about asking when this will be ... nobody knows.
There are ways to limit LR to 4 cores and that may improve your performance. I don't have the link on hand ... search this forum for it.
What size (in pixels, not inches or centimeters) is your monitor?
What size (in pixels, not megabytes) are your photos?
Are you doing lots of brushing and/or spot healing on photos?
It's good to know that program is useless and at time of multihreading ADOBE still cannot use it in favor of user
Monitor: Eizo resolution:1920:1200
Size photo: 6000:4000
I use brushing and "or spot healing on photos" i don't know this?
Given your answers, I think McLion is on the right track.
Ehhhh thanks Adobe go work!