Another factor that plays into the discussion, perhaps under the heading of "shooting conditions", is the aperture at which the exposure is made. If one is attempting to achieve maximum detail resolution, the "optimum" aperture for the lens in question (f8, f11 ?) will always be used, and shutter speed adjusted accordingly. Unfortunately, other factors, such as wind, often get in the way of producing maximally-sharp images.
One of the things that differentiates Leica lenses is that most are good to excellent wide open, and just get better as you stop down toward the optimal aperture. As a result, it is often possible to "get a shot" with a (hand-held) Leica M that would not be possible with some other camera/lens. Often, however, shooting wide open also pushes the resulting image into the realm where other image aesthetics may be more important than pure resolution. This is the realm in which the (legendary?) 75mm f/1.4 Summilux and the 50mm f/1.0 Noctilux excel, even though the pure resolution of either lens is not at its maximum.
Within the context of this discussion, however, I'm still not sure that the qualities of the lens will over-shadow the size of the negative.