Really doesn't matter. You just need to have at least 1 card that is large enough and able to load the dag alone. I have 6 rigs this is functioning on, all were 6x Rx470 4GB rigs, but then I took out a card in each and replaced each slot with an Rx580 8GB once I discovered the fix. Distributed the set ups so every 4GB rig has at least one 8GB card to load the dag. I have not confirmed if an Nvidia card can assist another Nvidia card in this way, I don't any under 8GB however the even stranger thing about all of this is that a p104-100 8GB will assist my Rx470 4GBs and they will mine.