Not just one recommended Graphics Card, but a comlete list of certified Cards you can find on our website. www.siemens.com/gtac.
Also befor you replace (your expensive) Graphics card, you might want to check the recommended drivers. As I know a lot of my colleagues use this K4000 card without problems. So the card should not be the problem. Newer drivers might solve the issues.
Versions of NX are not listed, as the driver are certified for all supported versions of NX.