Originally Posted by AaronP
No. The problem is that the NVIDIA driver has to make each metamode look unique to the X server. With DynamicTwinview enabled, you could add a metamode that clones two monitors with the exact same size and refresh rate as the single-display metamode. To the X server, these would appear as the same mode. The driver has to make the modes look unique, and the refresh rate field is the only way to do it.
You can query the actual refresh rates of the display devices in a metamode through the NV-CONTROL extension.
This sounds like a bit of a hack. The open source drivers manage to do dualhead whilst still reporting the correct mode to the X server, this seems to be one of the (very) few areas where they are better than the binary driver. Is this something that will be resolved when the nvidia driver finally gets proper randr support?