Hello. I currently have one rig which is 6X Sapphire Nitro+ RX580 8GB which I bought pre-made and I want to build a second one from scratch now, but I'm wondering what is the difference between models of these graphics cards? As I'm pretty much new to this and want to learn now about bios modding and get some experience there.

I see alot of RX 580 cards on sale, some are cheaper and some are pretty expencive. For example, Sapphire Nitro+ RX580 8GB is currently priced at $675, while ASUS RX 580 DUAL is $40 less than Sapphire one. And there is also some other models like Sapphire PULSE, Gigabyte, XFX GTS XXX, MSI Armor and few other models which are cheaper and/or more expencive.

Can someone please just simply explain to me, what is the difference between these models? Like is there a difference in modding bios? Or is modding bios on some of these cards harder/easyer? Are some of them giving less hash? Because I don't know much yet, and I don't want to make a mistake so if anyone could please tell me. And also advice if I should go with 8GB or 4GB version now. Thank you in advance.