Different GPU's in the same rig
I understand that this is not optimal, but how will i know that the cards are compatible with each other. And will i come across issues with the drivers?. Let's say all the cards at least was from nvidia like one 1080TI and three 980's.
You can mix devices as long as they are compatible with the driver in Hashcat. You can mix devices of any type as long as it is supported by hashcat. You will want to use the Nvidia 381.x driver else Hashcat will not enumerate the device name properly. With that, as long as the 381.x driver supports the cards you are mixing then they will work in Hashcat