The issue here is not a hardware one at all... You hit briefly upon the real issue...but the VRAM has nothing to do with it... The drivers use the pagefile to adjust to whatever the hardware VRAM of the card is this is part of the API layer that allows a modern game to function. What occurs though is that the Windows Default is that it is on your "C" drive and that it is managed by Windows... Both not good... so go into your, Control panel/System/Advanced System Settings/Advanced tab/performance/settings/advanced tab/virtual memory/change you will find that windows has defaulted to the "C" drive... and that it is being managed by windows... this you can do a few things that solve the issue.. You have 16 GB system memory... You want a custom sized page file 8GB Min (initial) and then up to your 16GB Max. you need to set the PAGEFILE to a different drive than your O/S and when you do this it will require a re-boot. Come back to the same place after to confirm the changes in the pagefile. That should stop the the pregnant duck effect, and reduce lag as well as give the drivers more virtual memory... The game is a 32 bit application. There are review after review at HardOCP and Anandtech that show VRAM does not effect frame rates in fact the 4 GB cards are no real help other that at extreme resolution (IE Exceeding 2560 x 1600) HardOCP did it with a heavily modded skyrim as well..
