It is likely the view distance that eats alot of it, I had a GTX580 1.5GB and played all max at 1280x1024, then went to GTX560Ti 1GB, and every 2 minutes it would choke as it run out of VRAM and had to swap it out, during this time the game would run at 2fps for up to 10 seconds, and i was killed
I then went to GTX560Ti 2GB and it runs like a dream.

Regarding the question, view distance lets you see further, enemies, traffic etc, and especially helps during helicopter fights.