I have a fixed freq monitor and specialized video card. In RH6 I have X running fine (took some work to get sync rates figured, but i got them) I am pretty sure that if I had a place to enter monitor information before 6.1 started the install gui, I wouldn't get an amber light on the monitor sortly after the screen went blank (meaning bad sync rate)
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Xconfigurator rewrite issue
Not only - specific data entry would also touch the install, who would have to provide entry of these.... Personally, I think choosing text install for such hardware is an OK option which would then make it Xconfigurator's task after the install.
current versions of Xconfigurator support entering exact timing information for your monitor if you so choose.