Ok, I'm having the exact same issue. I had a 7600GS which I got working, primarily with NoVertRefreshCheck set. I put in an 8500GT and no matter what other options I set nor what mode I try using, my Sony 1080i Tv won't sync over DVI. Without NoVertRefreshCheck, nothing above 720p gets validated.
I've seen many people discussing this issue and I've seen a few driver versions come out since the original report but I haven't seen much response from NVidia on the issue. I'm getting a tad discouraged.
EDIT: Ok, I managed to get a working 1080i mode. My modeline:
ModeLine "myATSC-1080-60i" 74.24 1920 1960 2016 2200 1080 1084 1094 1125 Interlace +hsync +vsync
And the options necessary:
Option "ModeValidation" "NoDFPNativeResolutionCheck"
Option "ExactModeTimingsDVI" "True"