Re: 7664 and 1600x1200 (maximum pixel clock?)
Respectfully, I don't think so. Notice that in the first case (7174) the log says CRT-0, but in the second case (7664) the log says DFP-0. As I mentioned before, most cards have a RAMDAC (the CRT output circuitry) that runs a lot faster than the TMDS signaller (the DFP/DVI output circuitry). The real difference is that the 7174 driver didn't correctly use the TMDS timing limits when connecting via DVI. I wouldn't be so sure that this is a bug.
An nVidia rep did comment that the driver doesn't properly account for reduced sync timings in an earlier post in this thread. Personally, I think it does the "right thing" since it will work if you define a reduced sync timing modeline. Ideally, the X server and driver would realize somehow that it should use some predefined reduced sync timing modes when connected to a DFP though.