Fujifilm GF 110mm f/2 R WR Aperture Series: Church Mosaic (Fujifilm GFX)
See my Fujifilm GFX wish list.
This scene tests the Fujifilm GF 110mm f/2 on the most demanding target I know of: a finely detailed geometrically planar subject at distance. Such a scene is unforgiving of focus shift or field curvature or any lens symmetry defects; it is the acid test for gold, or silver or lead—optically speaking.
Fujifilm GF 110mm f/2 Aperture Series: Church Mosaic
Includes images up to full resolution from f/2 - f/8.
On an optical basis, I have no hesitation in giving my highest recommendation to the about $2800 Fujifilm GF 110mm f/2—this is the telephoto lens that anchors the system. For most usage the GF 110mm f/2 should be preferred to the GF 120mm f/4 for the extra two stops of light and the smaller/lighter form factor. Plus, so far the 110mm f/2 has shown itself to have much more accurate autofocus with only a trace of focus instability.

GFX 50S + Fujifilm GF 110mm f/2 R LM WR @ 90.5mm equiv (110mm)
[low-res image for bot]