Hi Gziele,

GOU speed 1050 is indeed a bit higher than the specs we have online, but sometimes when it is safe we like to provide a bit more 🙂 Memory speed is “normal”.
Artifacts are usually caused by memory or software. When your graphics card runs well thru a Furmark and 3DMark test, the chance that the Graphics board is the cause of your problems is extremely small. Sometimes something as simple as a Windows Update can cause strange issues. 
Software:
Please make sure the Bios of your mainboard is updated. Then run all available windows updates, make sure to also update the Microsoft .NET Frameworks which is often optional.
And you can boot pc in safe mode (by pressing the F8 key at boot), than remove all Graphics related software, in your case most probable the Catalist software and driver. In safe mode the system can also clear the registry that is important. When your done, reboot the system in normal mode and windows will suggest ot install driver for your VGA, just click that away and go for the latest available driver download to: http://support.amd.com/en-us/download
When software is the cause of your problem, the above should fix it. 

Hardware:
When you have more than 1 internal memory modules, please try the system running on just one and/or the other to see if that has any effect.

Best regards,

Marcel