A few rather sweeping generalizations. I accept your observations for the that particular subset of Nikon lenses, but this is not necessarily true for all lenses from other makers.
I'm not talking about 2 stops different, but one stop less is acceptable with modern "great-till-iso3200-or-beyond" camera's.
The thing is, statistically when I go through hundreds of lens tests from 1970 - today, the one with the biggest aperture 8 out of 10 times looses from the second biggest aperture one when it comes to sharpness, vignetting, coma and flare, no matter the brand. The situation where the biggest one is the best is the exception, not the standard. But the big one will look like lensporn for sure.
Other samples I tested in house:
Nikon 50mm 1.4 vs 50 1.8: 1.8 wins on sharpness
Nikon 70-200 vrII vs AIS 80-200 4.5, AIS wins on sharpness
Nikon 28mm 1.4 or 2.0 AFD/AFS vs AIS 2.8: AIS 2.8 wins on sharpness
Nikon 20mm 2.8 AFD vs AI 4.0, AI wins on sharpness.
I could make this list very long....
Most of the time I have the large ones because of the AF, but if I have time to compose the picture by hand, the smaller old ones all win on corner-corner sharpness.
And nothing looks sexier than a D800 with a 85mm 2.0 AI.
