The status of my horrible stutters with newer Nvidia driver is SOLVED. For now anyway.
All I had to do was lock my framerate. I had really grown used to my 30+ framerate, and since the very act of locking causes a performance hit, I've avoided trying it. It's an acceptable fix for now, so I'll just have to be satisfied with 20-25fps.
On the positive side it's a totally smooth 25fps, much smoother than locked could ever be, and now that I fly that way the smoothness makes the lower framerate feel ok.
Since my frame cap is pushed down I can use higher levels of AA and not see a performance hit. At 1600x1200 with my overclock I can use the new 8xSQ mode in the 2.4.2 nHancer, which is 2x2 supersampling with 2x multisampling. It sure looks nice when supersampled in both directions.
Overall I'm just pleased I got it fixed, even if it does mean lower framerates from now on. Maybe I'll get a Nehalem system in a few months and then everything will change again.
Here's a shot where I'm pegged at 25fps.