I am a little surprised to read that a Visconti nib has a "superior nib" to a Parker Duofold.
I have two Parker Centennials. I think they are the most beautiful nibs I've ever seen short of Waterman Carene (I also have two of these). Or maybe Edson - which I cannot afford.
After I got the two Centennials, I formed an opinion that they were/are one of the most incredible performing nibs. I special ordered both nibs (nib swap from the Janesville plant) when I got them back in the 90's when new. Both had plain medium nibs originally.
One is a Left Oblique (No. 89) which is a stellar writer and used as my go-to correspondence pen. Butter smooth, incredibly expressive, and a pleasure to use every time I pick it up and look at the beautiful nib. Makes any ink look better and provides a "shading" platform for the inks that do. Makes even my average writing look better.
The second was swapped for an extra fine (X) with a request that it write with good flow. It got specially tweaked at the factory in Janesville and writes - smooth as butter. I have to watch the ink it uses as Waterman Black, for instance makes it into a medium writer. But again, a wonderful, beautiful smooth nib without the slightest "catch" or scratch even as a X nib.
I am thankful I got them everytime I use them.