Velvia has a truncated color range and over saturates what colors it does represent while Kodachrome has a much smoother and complete range of color, but goes ballistic with reds. I have great KM-25 stock and the only difference I see between it and 64 is slightly finer grain and a tad smoother color range than 64. But they are so darn close that I could have easily passed on 25 and shot even more 64 for price and consistency's sake.
I have shots from New Years 2010 in Times Square that have outrageous color, but not funky and truncated like Velvia would have did, it is really neutral, but spectacular.
I shot it with a Hasselblad XPan and the 30mm aspheric, Nikon F100 and 14-24 2.8, M3 with 50mm 1.4 asph and a M6 + 35 1.4 asph. All did really well with the film, the Xpan having lower contrast that handled high contrast scenes better and the Leica having fantastic contrast and superb color saturation making it outstanding in low light.
I just projected the 24x36 images about 30 minutes ago using a Leica Pradovit RT with a 90mm Super Colorplan Pro lens, there is nothing that can touch Kodachrome, not even close!