My GTX480 got 35fps (99% gpu usage) at same resolution
when this demo was beginning. My GTX480 VRAM got max 1360MB.
Your GTX465 can't exceed to 1024MB due to max 1GB.
But I recommend that you drop resolution to 1024x640 to improve performance.
You like max high-end videocard of generation (your old 8800GTX) but your GTX465 isn't max high-end of generation. Why??