100% CPU is caused by the driver/SDK versions. Some versions are perfectly fine and experience no CPU bug. Other versions are plagued by the CPU bug perpetually, and should not be used. Still other versions seem fine, but still have the CPU bug at high Intensities. This last case can be quite sneaky and confusing for some.
For 5xxx cards, your best bet is to uninstall your current SDK, install the newest drivers (12.8 ) WITHOUT the included SDK, and then manually install 2.5.
Nobody can read, its official.
We can read. If you'd like to give us more information about your OS, drivers, and SDK, maybe we can help you a little more.