According to many on this forum, 4gb is a bottleneck. These vrammongers have mostly been banned though for spewing vram threads. 4gb is enough nowadays, so is fast gddr5. That's why nvidia is holding out for HBM2. There's really no need to go HBM atm, when gddr5 is fast enough. By the time HBM2 hits the market, it might have some use. Might.