Have them read this over from the vendor: http/helpcenter.graphisoft.com/technotes/video-cards/recommended-video-cards-for-archicad-20/
Its not a lot of difference between all of those cards but depending on project size you will see some pull ahead a bit. I would show them this and let them decide.
I know those charts, it's just about entry-class desktop GPUs. My friend has to choose between GTX 960 and R9 380. R9 380 has more computing power, but will it perform better than 960 in ArchiCAD? Will it be more dependent on memory than gpu power? Those are questions I seek answer for