Thing is, development over the last ten years or so has moved so fast that it makes knowledge obsolete fast. It's a good idea to stay away from stainless-bladed swords, generally. And I used to be very wary of 440C anything, as well.
However, 440C can be a fantastic blade steel if the heat treat is correct. Most of the junk made with 440C is not properly treated, so it fails. I bought a lot of cheap Asian junk with 440C blades (or what were represented as 440C blades) when I was a child, and I eventually grew to distrust it.
Similarly, although stainless steel is generally too hard to temper to make a good sword blade, I can believe that ATS-34 would work, especially in heavier blades. ATS-34 is technically stainless steel, but its carbon content is more like carbon steel. It's what many call "barely" stainless. And it doesn't resist corrosion as well as some of the higher-chromium "true" stainless steels, nor does it go to the same level of polish, but it's also generally tougher and behaves more like high-carbon. I haven't had the chance to forge it, so I don't know what it feels like under a hammer, but I haven't done much with stainless of any type. Leave an ATS-34 blank out on the back porch a few days next to a 440C blank with the same finish, and you'll see the difference when you bring them in. "Stainless" and "high carbon" overlap a bit nowadays.
As pointed out above, Jerry Hossom and Paul Bos can create a good sword with stainless steel, but those two together could probably make a pretty good blade out of Flintstone vitamins if you gave them some notice.
As for cutting a silk scarf in the air, I can believe that there were blades made of Wootz that could do it. I just think it likely that it was the blade geometry and the polish that made the difference, and the same thing could have been done with just about any steel, including iron. I don't believe in a knife you hold edge up and cut a silk scarf by dropping it onto the edge, but with a good slashing design with lots of curve I could see a man slashing a scarf in two. It would still take a superb cutting/slashing design with a thin edge and a long edge, but it could surely be done and after all a lot of knives one would have found in Damascus back then were designed just that way!
When I was a kid, I used to love to read "Choose-Your-Own-Adventure." There used to be one in which you were a time-traveler who traveled back on a mission to acquire a sword belonging to Miyamoto Musashi. In it, a swordsmith berates and even strikes his polishing apprentices because, although he can drop a silk scarf onto the blade of a finished katana and it will drop instantly in two neat pieces, there are still a few ragged threads along the cut. A few minutes later, the Samurai who picks up his sword chooses you on which to test it and you have to escape.
It struck me as a bit strange at the time, and I was only about ten then, but like many others I just assumed the author had done lots of research.
