Hum... na ATi FAQ:
Estranho ficares com a máquina sem responder ... :\2. Client looks like it is using lots of CPU time: Graphics drivers must poll the GPU to see if it is done. This will look like a lot of CPU time being used, but nothing is really being done, so one can run other relatively CPU heavy code at the same time. However, we do not recommend running multiple FAH clients, as this can significantly slow down the GPU client. A good rule of thumb: leave at least 25% of the CPU time available for the GPU client.