You can find more details about recommended hardware on Help Center. You can find a list of recommended graphics cards at:
Hardware for Archicad 20 Recommended hardware Mac OS X 10.8 Mountain Lion and older systems are not compatible (Archicad cannot be installed).Mac OS X 10.9 Mavericks is compatible but not tested by Graphisoft.Windows Vista and older systems are not compatible (Archicad cannot be installed).Windows 8 (64-bit version) and Windows 7 (64-bit version) are compatible but not tested by Graphisoft.Operating Systems for Archicad 20 Recommended Operating Systems