The choppy performance on Geforce cards is driver related.
To fix the problem simply install 40.72 drivers instead of 41.09

People with low end sytems like me should use these settings:
1. Choose "High image quality" in your vid. card's Direct3D properties.
2. Use 1024x768 res & 16-Bit color
3. Choose fast gamespeed
4. Enable DMA on hard drive & CD-ROM
5. Choose on the pitch sound
6. Disable background programs(Except explorer ans System Tray)

My System
Athlon XP 1800+
512 PC2100 DDR-SDRAM
ABIT Siluro GF4 Ti4200 OTES 64mb
ECS K7S5A Mainboard
Seagate 40gig 7200rpm Hard Drive

lol i got a full optimized PC..I cant say tha it is Choppy ..It got 80frames/sec avg but not perfectly smooth motion.I use render string and medium detail ..and this fixes the prob almost..

The game performs much better with 40.72 drivers.
As for frames per second I bet you that you could have 90fps and the game would still be choppy.

What render string do you use? All the ones Ive tried do nothing.
except the "render every ai = 1" made everything go in slow motion.