Technically, xorg is the windowing system, and compiz is a layer ontop of the server which allows for 3D effects.
The high CPU usage is likely indicative of software rendering instead of hardware rendering.
As mentioned in this question, you can run /usr/lib/nux/unity_support_test -p to see if software rendering is being used. If so, you'll see something like:
Not software rendered: no I'm not familiar enough with where the AMD APU support is these days with regards to 3D drivers, but I'd check the additional drivers and see if there's any updates for fglrx or fglrx-updates, which should then enable hardware rendering, and reduce the CPU load.
If you want more of a boost, disabling some of the visual effects could help. CCSM can help with that:
sudo apt-get install compizconfig-settings-manager compiz-plugins-extra After installing, you can just search for CCSM, and that'll let you disable some of the visual effects, which may help you get performance back.