Yes, theoretically that is the case, however the only time I've ever pushed the VRAM that high is using huge particle systems in C4D, iRay or Octane rendering, or running multi-monitor games at resolutions above 2560x1440. Right now, honestly I think the 6GB may even be overkill. Even in pretty large AE raytrace scenes I'm still using just a fraction of that vram. Better to go for more CUDA cores, although it's nice to be future proofed though. I think it's still a case of software needing to catch up to hardware potential.
-TG