is an interesting issue, I can see by the post you have made and your join date, is not your first rodeo
would be curious to see what equo --install --ask kde-meta would show
I am currently on gentoo, kde 4.6.3 I have desktop effects enabled and xbmc running as my music player.
firefox, several tabs open and a couple terminals. cpu is about 20 - 25%
I think this is high on a quadcore cpu for what is open, I ran the same on a p-4 3.2 cpu, used about 10%
But a few 6 months ago, kde updates, and kwin is a pig.
If kde-meta was already installed, in theory, kde-meta would only install one package, kde-base
So if it installs a bunch, you was missing several packages.
On the other hand, are you sure this is a kde issue and not a video driver issue?
You did eselect kernel list and it matches uname -r
eselect opengl list is set to nvidia
xorg.conf is set to nvidia
Just asking since a recent nvidia update may have changed opengl .... I sometimes forget to check the basics