Yeah I think it has a 5000 something series GPU. Not the RX 5000, the old kind. 
5770 series
macpro 2008 ( version 3,1) under manjaro , need alt to change disk on boot ( refind by @apple 
)
I got the HD 5870. Original card was the HD2600 XT. You know, the card that was infamous for getting clogged up with dust and overheating.