FWIW, I just shot the fall colors in upstate NY last week. I used a roll of Portra 160 in my Canon P, and a roll of Ektar in my reversed lens Brownie Hawkeye. The colors and range of the Portra were really excellent; the Ektar was wild and saturated, but striking. If accuracy is your objective, go for the Portra; if you want to make the colors pop, Ektar it is.
I'll probably be back out this week with a roll each of Portra 160 and Ektar in my Rolleiflex. I am curious to see how they behave with the camera variable removed.