I was having the same sluggishness in kde4 (due to high cpu by xorg) and I resolved it by changing the qt graphics system to raster. You can make the switch by:

1. install kcm-qt-graphicssystem
2. go to Configure Desktop > QT Graphics and select raster
3. log out and log back in

Some programs don't work properly with raster but you can start those programs with the native system. The only one I'e had problems with so far is ibus, so I start it like this:

QT_GRAPHICSSYSTEM=native ibus-daemon --xim
The only problem with ibus was that the icon in the system tray was invisible but it was fully functional.