Thanks for the interesting example. It mirrors well my own results. You make a good point showing that f/22 on a 6um back is not too bad. When you shoot low contrast structures that are imaged large it hurts less too, compared to say a brightly lit detailed city at a distance.
Side by side with a shot made at f/11 at the plane of focus would show a significant difference though, and if making a print it would not look that much worse if shot with 9 um pixels, hard to differ would be my guess.
There's more with you though, this techy test shows that with proper sharpening techniques you can sharpen f/22 images to very closely resemble f/8 or even f/5.6 images, and that with a D800 which has even smaller pixels:
The Diffraction Limit. How Small is Too Small? - On Landscape
(I think they underestimate the low frequency effects though which affects the global sharpness impression). Digital sharpening is much more powerful than tools available when shooting film, so we can push diffraction further now.
Anyway, what people with high res backs often choose to do is to rather than shoot f/22 like they perhaps did with their old 22 meg back to get deep DoF, they shoot at say f/11 or even f/8 with the focus plane at something important and let it slip visibly out of focus (at nosing distance at least). While this style seems more relaxed in terms of DoF it requires precise focus placement to get the desired result (laser distance meter and high precision focusing ring of the pancake cameras). This way you get to appreciate the peak resolution of the system where the focus is set, at the cost of a less evenly rendered scene in terms of resolution.
I prefer to stop down more to get more equally rendered resolution, unless I want a short DoF effect I don't shoot larger than f/11. I'd guess something like 70% f/11, 20% f/16 and 10% f/22 - f/32, tilt used very often. It works well with a view camera focusing on ground glass (I use a Linhof Techno). I have 7.2um pixels today, I'll use the same style with 6um pixels.
It would be interesting to know what is taught in the MFD landscape shooting classes these days.
Although it might seem like we disagree in most things here, I think we are quite close in how to deal with DoF in practice, ie not be too afraid about stopping down. What I talk about here is that if one spends a very large amount of money on a very high resolution system one may want to choose a shooting style that really maximises that potential, and I see that many do. I also think that if one prefers to stop down more (like I do) it may be worthwhile to look into older generation backs as a more economical and balanced solution (I also like the distortion-free light f/11-optimized Schneider Digitar wides); while it's true that higher resolution system renders better results even when stopped down, the difference becomes rather small.