It mainly depends on the games you play. Open-world games like Red Dead Redemption 2 tend to consume a lot of video memory and quickly populate 6GB in a 1440p resolution. FPS titles generally take fewer amounts of memory but require a high framerate for the best experience, so again 1080p is recommended. Most 6GB cards are more than enough for high-quality 1080p games with high frame rates. If you want higher resolution, 8GB cards like the Nvidia GeForce RTX 3060 Ti or RX 5700 XT are ideal.