The only mode that is "stutter-free" on the GeForce 6800 Ultra for me is Extreme Performance
The following performance monitor results are based on a 60 second walkthrough on the Isle of Refuge at four different display setttings - Very High Quality, Balanced, Very High Performance, and Extreme Performance.
Statistics were captured at 2 second intervals and confirm that the stuffering is not related to a CPU, memory, or disk bottleneck.
Resolution of 1024x768 with 4X AA / 8X AF. EQ2 is installed on the E: drive.
Very High Quality
Very High Performance