No, windows confuses you with the shared 4GB of Vram, video cards have always been able to map to system resources, games normally do not allow this however because of the impossible lag that would incur.
The shared memory is system RAM, theoretically, that can be used.
Looking at your GPUZ screen shot I see it lists 0 and 0 for the current GPU speed and RAM speed. Did you try and flash a 4 Gig card with an 8 Gig BIOS?