Just a quick note about my statement re 35mm film and a 39MP back. If you dig, you will find a shootout performed by Don Hutton on the LF forum where he went out with a friend who owned a P45 and shot some very controlled tests with a Leica MP, a leica ASPH lens and Adox CMS document film and then scanned with a drum scanner. He also got out a very high powered microscope to examine resolution charts shot with this camera/film/scanner combination. Bottom line was real resolution above 100lpm, which the 39MP back can't do.
Now all that said, this combo is pretty limiting. It is black and white. It is slow film. No way would a professional want to use this for any sort of volume work. But if you are doing photography for your own account and on your time, the point is that there are more options (and less expensive ones) to achieving super high print quality than running out and buying the latest digital back.
My point with the initial post was that the test was not done in a way that optimized and really showed what an 8x10 can do. The scan sample rate was at least 1/3 of what a typical 8x10 setup is capable of resolving with normal film. Come on, less than 1000dpi? Every test I have ever seen done on sheet film indicates that there is probably around 2000-3000 spi of real resolution on 8x10 film if it is shot at optimal apertures with good modern optics.
I am not saying that anyone should run out and buy an 8x10 with a brace of Sironar-S lenses and a Aztek Premier drum scanner. Shooting 8x10 is a pain in the ass, and it has some of its own inherent limitations. You are always fighting the battle between depth of field and diffraction-induced resolution loss because of the long focal length lenses needed (a 'normal' lens on 8x10 is 300mm). It is heavy, demands the use of a tripod and a huge bag of film holders. You fight dust, alignment issues, and all sorts of other challenges.
But there are more options for getting truly high quality digital files than spending the amount of money that would buy you a nice Beemer on brand new digital back.