One thign is a card with 1 GB or 2 GB, other thing is the chipset it uses. Try using high settings, and medium to test if its stable.
Virtual memory keep at leat 1024 MB.
Well, I dont know how the virtual memory settings affect VRAM though both are not related, provided I have plenty of Physical RAM. However, I can check with settings reduced, but again is this the only solution? or any specific nvidia driver can help?.