Because of the resolution and program limitation, all heavy games with Full HD resolution used under 1GB capacity VRAM.
1.5 GB VRAM is the best design with 192 bits! Optimized 3 channel 192bits (60GB/s) memory bandwidth!
2 GB VRAM is lower bandwidth with 192 bits! Slower 2 channel 128bits (40GB/s) lost 33% memory bandwidth!