Agfa made a 25ISO colour neg film about 20 years ago. The grain was almost non existent, but the contrast and colour saturation was off the clock. It had zero latitude in both the exposure and development stages. It was sharp as hell but totally unmanageable. I think I used it twice then never again. Almost a forerunner of Ektar in all respects.
Like you I am resorting to Portra after this but if it doesn't come up to scratch it is back to Fuji again
Were you thinking about Ektar 25? I used that about 25 years ago. Very fine film. No grain. Here's a scan. http://flic.kr/p/921HSF