[you2]

Interesting. I thought one of the soon to be released GFX cameras was going to have 100MP. Then again those lenses (while a tiny bit larger than FF) seem to have much better corner sharpness so maybe it will work with that camera ? Then again maybe my memory is faulty ?

People get pretty good results with the 5DS ( R ) too. OL MTF results skew the perception a little (partly due to sharpening). 
Do you have any comparisons between those GFX lenses and lenses on higher res. "FF", which show a much better corner sharpness across the board?

Tough questions as not very many sites have reviews. Here is one that shows the 45f2.8 is pretty decent:
https://www.imaging-resource.com/lenses/...wr/review/
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But it isn't a great review. General reports have been that the lenses are fairly sharp edge to edge. Then again we would have to compare them to the better ff lenses and that is pretty hard given the number of soft consumer lenses in the mix. Most of canon very best lenses are actually the pro zooms or super tele which are not very comparative. Sony lenses have been pretty soft and sigma best lenses have been short tele. I think the general vibes on the 45mm (35? 30? ff) is very positive across many sites.