(Disclaimer: lens for sale)
We use the HC 120M II (improved IQ over 1st ver) on our H5D and GFX . Great lens, goes 1:1, no CA, sharp as hell. We'd keep it, but it's over-kill for us.
Very easy to focus manually and works with tubes. The orange dot copies will AF on the X1D, but they're far more costly and with focus peaking, etc, AF is really not necessary.
The only things that would make me hesitate on the XCD 120 are a) there have been many reports of issues with focus failures, DOA lenses after little use etc., b) it doesn't go 1:1 and c) cost for what seems to be the sole problematic lens in the lineup for some reason.
The Mamiya Macros are also an excellent option, but with no leaf shutter, you'd be stuck with the slow E shutter of the X1D which could be problematic.