I think Bill's test results are useful in illustrating tendencies, not absolute in the real world but something which the photographer should be aware.
Some time back I looked at theoretical maximum lppm at various apertures, and used these as a rough guideline for selecting the best camera system for a particular application. I tend to use 8x10 for infinity shots; grand near-to-far landscape compositions amenable to tilt; and intimate scenes which require little depth of field. Otherwise I will use a smaller format. On balance, I have found 4x5 more gratifying for landscape work than 6x7 (I own a Mamiya 7 also) because I keep running into depth-of-field limitations with 6x7 normal and moderately long lenses due to lack of movement capability (WA lenses are OK). Since IMHO I get better results with 4x5 @ f/45 than 6x7 @ f/22, I typically use the M7 only when I need it's portability or ease-of-use, or need to shoot without a tripod.
Of course to get the most out of 8x10 you need to use top-notch lenses, which many folks do not. I'm getting significantly sharper infinity shots with my relatively exotic APO Tele Xenar convertible than the popular Fuji 600C and Nikkor 800/1200T. On balance I get sharper results (particularly at the edges) with my 300mm APO Sironar-S than the popular 300mm Nikkor-M or Fuji-C. Most folks figure enlargement factors are smaller with 8x10 so they use cheaper lenses, which is fine for contact prints but defeat the purpose of using the format when enlarging. I do relatively large digital prints (30x40") so increased sharpness in the negative does show up in the print.