4GB is enough for literally right now, where 99% of us are still using 1080p/1440p monitors, and just barely.
From benchmarks I’ve seethe Fury X is consistently beating the 980ti/Titan X in benchmarks at these resolutions, but as soon as you bump it to 4k/8k resolutions the absolute limit of 4GB starts to really become a bottleneck compared to 6/12GB, next generation of AMD cards will likely have more memory due to this, but it’s not a barrier for most gamers right this moment.