The whole scene
Centre crop - click to open in new window at correct size
2/3 of way out to upper left - remember to click for actual size
3/4 of the way to upper left - and click
extreme upper left - yet again
So, this is f8 in a real subject, not a flat plane. Lightroom used its profile for this lens to correct for distortion and I had to add some extra purple defringing so this is what one would actually have to work with. Clearly the corner is not great, but remember this is a tiny part of the picture. I made a print, 41X55 inches, or at least the corner thereof, and the 13X19 print of the corner is sharp from 6 inches in - this looking at a 5 foot print from 10 inches. Do I wish the corner was a bit sharper, sure, but I can live with it. In practice, this means that with the Pentax 645Z I can make a 41X55 print that looks as good at the same viewing distance as a 24X36 inch print made with my Canon 5D2 and 17-40 at 17 mm. - so almost double the linear dimension (24 to 41). Essentially that's what I was looking for.
This is 100% even without clicking, but you see more when you do, of the same corner, but at f16, and a little bit more sharpening in Lightroom (70, .8 instead of 50, .7), also a bit more shadow recovery.