I think that some of the comment that faster lenses preform worse than the slower counter parts is a little off.
It's a well established fact that, in the past at least, was acknowledge by the manufacturers. Zeiss was happy to say that the 80mm f/2.8 Planar was an excellent lens and as good as they could make it but, the 100mm f/3.5 Planar was even better because it was slower and they didn't have to push the design for the extra speed. Back in the darkroom the Rodagon 50mm f/2.8 was the defacto standard for printing from 35mm. I still have one. I also have the more expensive 60mm f/4 Rodagon that Rodenstock made very clear was the better lens.
Stopping a faster lens down of course improves its performance. But that doesn't guarantee it will then be the equal of it's slower sibling (also stopped down).
There have always been exceptions to the rule, for example when the manufacturer deliberately makes the slower lens cheaper, but as a general rule it holds true.
Joe