I think that you are right. I think that the newer drivers are enforcing a limit that my particular card seems able to exceed. I wanted to also thank you for the "ExactModeTimingsDVI" suggestion. That was an important part of getting things to work. Thanks!
I have still not been able to get things working properly under windows.
I've tried powerstrip and the advanced timing controls under the nVidia 71.89 driver. When I enter the same timings that I used in Xorg under Linux, my monitor display is, well, "messed up".
It looks like each scanline is about 75 or so pixels short so the image wraps strangely across the monitor about 50 times from top to bottom. The strange thing is that the exact same numbers work when entered into Xorg (with "ExactModeTimingsDVI"). Obviously the drivers are doing something with those numbers behind the scenes...