the 8GB version runs at 8Ghz (8Gbps) effective while the 4GB version runs at 7Ghz (7Gbps), not a big difference and you can still oc the 4GB version, id still recommend getting the 8GB version as some newer games tend to use a lot of VRAM, take for instance Battlefield 1 Multiplayer, it uses over 5GB at the max settings @ 2560x1080, and i believe more and more games will start to use more than 4GB frame buffer