I understand your problem. I have been wondering for some time now how Nvidia can say that the minimum system requirements for the Quadro 6000 is Win7 XP SP3 (or Linux) when the memory model is 6GB per card. At the same time they say you can get by with 1GB of system ram with 2GB being recommended. I have been editing 4k video (Sony NEX FS700) on a Quadro 6000 SLI system that just smokes through editing and rendering media but my system has 16GB of ram on a 64 bit OS. So Im not exactly sure how the memory address space concerns video cards in actual fact.
I think that the actual memory address space is tied more to resolution of the system than it is the cards available memory.