Yeah, this comparison isn't that useful.
The difference in VRAM is only beneficial when the game uses more than what is available AND when the GPU itself can keep up with the graphics settings.
The more important bit is: Does this game use more than 8GB or 12GB VRAM when the graphics settings are set to 60fps minimum for the GPU.
And the answer is, 128-bit memory bus GPUs aren't fast enough to benefit from more than 12GB for a vast majority of games. In fact, most of the popular titles still fit inside of 8GB VRAM, with only a handful of triple-quadruple-A titles having poor optimization that they spill over into 9-10GB or 13GB.
This is a problem that is easiliy solved with 3GB (24Gb) memory chips, but they don't exist yet so we are stuck with not enough at 8GB or excessive at 16GB.
On the other hand, 192-bit memory GPUs do have enough horses that they become limited with only 12GB of VRAM. However, they obviously can't be loaded with 16GB VRAM because you'd need a 2.67GB memory chip.