Jack One thing the DVI2PCIe card can do that others cannot (at least easily) is emulate arbitrary EDID data from another display. If different EDID data has bearing on what GPUs do is an open question but I certainly consider leaving the opportunity open for investigation a good thing.
Only thing I dislike about it is it requires either a Windows driver, or a distribution specific Linux driver, so it isn't ideal. VideoDiff currently works best under Linux, but optimizations in the future could be done for Windows.