Resolution notwithstanding, Ektar is ISO 100, so shoot it at 100. Don't shoot it 125, or 66. I did some testing, some others have as well. The thing is you can over expose it fairly well, but it will rapidly start losing saturation in a number of colors. They start turning greyish. This can lead to the impression of more detail, as you can "see" details on grey better than you can on a navy blue peacoat (in one online example, this was used). Just 1 stop and you can notice a bit. 2 stops and you start losing color. That may be why some people are unhappy with the colors.
You shoot it at the proper lighting and it performs well. The photo won't be ruined if you're over or under. It actually has a wide range. It's just that the "sweet spot" is rather narrow.
I'm an amateur and I can even spot this in my own test rolls.