Das ist so nicht richtig, steht sogar genau erklärt wie es sich mit dem Speicher verhält.
Zitat aus dem Artikel:
To optimally manage memory traffic in this configuration, we segment graphics memory into a 3.5GB section and a 0.5GB section. The GPU has higher priority access to the 3.5GB section. When a game needs less than 3.5GB of video memory per draw command then it will only access the first partition, and 3[SUP]rd[/SUP]party applications that measure memory usage will report 3.5GB of memory in use on GTX 970...
und
Perhaps folks will find some instances where the GTX 970's memory allocation limits affect performance more dramatically than in Nvidia's examples above. If so, maybe we should worry about this limitation. If not, well, then it's all kind of academic.