Thank you, Henning, for such an impressive study of color film resolution. While I don't have any quantitative data for comparison of Ektar to slide films, I have been shooting both Ektar and Velvia 100 and find them to be fairly similar in color rendition and color intensity (not a very precise term, I am afraid).
I have been enjoying the autumn colors here in Seattle and have taken a number of photos of the local trees using a Hasselblad with two backs: one containing Velvia and the other containing Ektar. I take identical photos using both backs and develop them myself (the E6 using the Kodak 5L kit and the C41 using the Tetenal blix-based kit). I print the C41 using a dichroic enlarger and make 12"x12" enlargements on Fuji CA type II paper (developed at room temperature using Kodak chemicals).
I am very pleased with the results. Both films give fairly saturated colors, which are not everybody's cup of tea. The Ektar contrast seems to be increased when printed on the Fuji paper and the combination has similar contrast to Velvia (viewed on a light table).