You wouldn't. And it's not a limitation unique to digital, as the pushed Tri-X to Pan-X comparison attempts to point out. The exact same thing is true of film. A 35mm shot on TMZ at 3200 for example, will never compare for sharpness, resolution, grain and tonality with a 4x5 on TMX, or 4x5 on anything for that matter. And the 4x5 won't compare to an 8x10, all things being equal (which they seldom are - lenses for smaller formats are often better than those covering larger formats, film flatness suffers in film holders compared to a pressure plate for roll film, but larger formats are much more likely to be shot with a tripod etc.)
Still, the limitations of the format, film, developer etc. that are used initially become fixed.