So this bad boy arrived just in time for Christmas. I've used the Contax CY 50mm f1.4 on my GFX system before but I think it is much more compatible with the 907X (looks-wise).
Center sharpness is acceptable wide-open, provided you can nail it. Sharpens up really well at f4/f5.6. I've never been concerned with corner sharpness in 16 years of my photography journey so I didn't check that.
Vignetting is acceptable and correctable at close distance. Near infinity, you will have to toggle the vignetting slider to +2.0 or +3.0 (C1P) or crop 4:5 to be clean. Overall not an issue for the things I shoot.
Raw files of simple sharpness test (f/1.4 & f/5.6) and vignetting (MFD & infinity) here, free for everyone to evaluate:
https://drive.google.com/drive/folders/1yGv0xDTKDuNNSHMS2-U-PDEWkYUcBVrD?usp=sharing
View attachment 179774
I finally managed to get my hands on a Minolta MD to X1D adaptor, pending shipping. Can't wait to adapt my 55mm f/1.7, 45mm f/2 and 100mm f/2.5.