Sepsu :
My friend is buying a new card off his friend and selling his old GTX 970, I have a GTX 970 G1 from Gigabyte not the same brand, has an extra fan, not entirely sure about the clock speeds or anything but could I SLI them? or does everything need to be the exact same, would I need another GTX 970 G1 from Gigabyte?
Yes, you can always SLI two of the same nVidia model cards even if they are different remakers (by remakers I mean people like Gigabyte, Zotac, ASUS, EVGA, ect just can't think of the right word atm). If they have two different clock speeds the card with the higher clock speed will automatically down clock itself to match the lower one. And as for VRAM, only VRAM on one card is used during SLI.
Hope I could help!