If I can veer a bit off course for a moment, the realities of todays games and tomorrows applications need to be discussed before going too far into the GC 4GBs successes and failures. With the optimizations in DX11, even the most demanding games are requiring less frame buffer capacity than ever.
Next generation DX11.1 equipped console development will bring the focus towards a further streamlining of game engines, so highly detailed environments wont require memory hogging, inefficient high resolution texture maps. As many game developers have already stated on and off the record, this will lead to an increase in the amount of raw processing power required to render a scene and a significant drop in the local memory requirements.
What does a situation like this mean to cards like the GC 4GB? Now and in the future, its core processing performance will likely become a bottleneck long before more than 2GB of 7Gbps memory is required to provide a smooth gaming experience.