It might also be the GPU can't cope with having to draw so many polygons and then having to draw them again, then again as the view changes. It will still be memory though - processes like that need buffers to work within. If you're on a laptop chances are the system RAM is shared with the video RAM. Some desktops with onboard, or onchip, graphics will use system RAM and vary it according to needs. I'm wondering if you can change something in BIOS to allocate more memory to the GPU. Is it by chance an AMD A-series APU in your system?