> If you're going to use only MorphOS - it doesn't.
That's only true for cards with AtomBIOS, i.e. R500-based and later cards*. So R400-based cards like the X800XT or X850XT have to be a Mac edition, or a PC edition re-flashed with PPC ROM.
Edit: * While early AtomBIOS versions came already somewhen during R400 series, the MorphOS AtomBIOS parser seems to require the newer AtomBIOS versions that started with the R500 series.