I though that this article did not fairly compare 4x5 Velvia to the Betterlight Super6Kand the P45. From the crops, the Betterlight looks clearly superior. The Betterlight shows greater contrast in the fine details.
The problem is that the chromes were only scanned at ~31 lines/mm (~1600 dpi). Velvia, when combined with good lenses, is capable of reproducing high contrast details in the 50 lines/mm range. (See, for example, http://www.hevanet.com/cperez/testing.html
, for lenses. Velvia has listed resolutions of 80 and 160 lpmm depending on the contrast.) I believe that had the 4x5 Velvia been scanned at higher resolution, finer details would have been visible. Obviously the contrast of those details would be markedly less than in the original--you can see the contrast dropping off at 31lines/mm--but they would be there. My experience is that if I scan at 1600 dpi, I miss quite a bit of the detail available on my best chromes.
The dollar bill at the size pictured isn't the best vehicle for looking at features smaller than 31lines/mm. The smallest features are about 20 lines/mm.
I don't know if the effect would be big enough to make Velvia "better" in many cases or not--I'd like to see the comparison. I suspect that Velvia would show a discernable resolution advantage, but the Betterlight would almost always look better because of its lower noise levels. (Of course you need a completely stationary object to use the Betterlight). Against the P45, I would guess the resolution advantage of the film would be readily apparent.
On a separate issue, I suspect the drum scan for the Velvia was not done to produce the optimal resolution. The aperture should be about the size of a pixel. However, the aperture is round and pixels are square, so adjacent pixels generally overlap a little. If you're looking for the best possible resolution for a comparison like this, the scan should be done at a higher resolution and then down-sampled.