On my extremely low end computer, I've been looking for good drivers lately. I found these beta drivers released on March 30th that have increased my fps with full view distance and MEDIUM graphics (I usually can not use those even) I have an 12 fps increase.
http://www.nvidia.com/object/win7-winvista-64bit-270.51-beta-driver.html
Highly recommended.
Thanks for the report. I knew of these drivers but have been leery of installing them. Something you don't mention, they purportedly fix the "sunglare-visible-through-landscape-and-structures" glitch many of us series-400 owners suffer.