All I can say is that the placebo effect can be pretty powerful. Also, I didn't do a proper test of it at the time. I had played through the demo in its entirety, then tried futzing with the config files. I must have gotten used to how the game felt at that point, so it definitely seemed better, especially for the few minutes I bothered to play again. I should have used an FPS counter then, but I was being sloppy.
I went back and tested it some more, with an FPS counter on, and there are some interesting things at play here. Possibly another thing that may have thrown me of initially, and it was absolutely one of the first things I noticed after changing the setting, is that unlocking the framerate actually let's the game's title screens and menu run at 60fps. Try it for yourself: switch it to 60 and just observe the title screen. It is much smoother.
Which is really weird. Setting the game to 60fps makes everything but the game itself run at 60fps.
Anyway, sorry for the confusion. I should have tested it much more rigorously.