I'm sorry if I caused you any offence, Felink. I didn't know that English isn't your first language and your profile doesn't give a location. Still i hope you took our humour in the spirit was intended. :-)
Generally speaking, I find that Kodak films record reds more accurately than Fuji, which tend to emphasise greens. Portra is Kodak's professional line whereas Fuji c200 is aimed at non-professionals. Expect the Portra to be more consistent with more accurate colour rendition than the Fuji. I'm not saying the Fuji isn't a fine film - I'm sure it is. I haven't used either, but I've used Portra 160VC, which apparently has more saturation than the new version.
For colour negative films, unless your camera's shutter is inaccurate use the manufacturer's recommended ISO setting because the manufacturers test the film and they know what they are doing. Why would they lie about their products? (Someone is bound to tell me I'm talking tosh here, but this has been my experience!) However, camera shutters aren't always accurate and many older shutters will run slower than the designated speed. Meter adjustments can drift dramatically over time. Testing your camera and meter will help you feel confident about using them. Use a properly-adjusted, hand-held meter for more accurate exposure readings.
Colour negative films have plenty of latitude, mostly in the area of overexposure. For the best results you should expose for the deepest shadows you want to see in a print, especially if the subject has a large dynamic range. Highlights will generally be fine but some details (sky details etc) may not print on an automatic printer and you may need a hand-made print or skilled scanning technique to reveal them. One stop of underexposure will give you thin negatives with grain and loss of detail in the shadows. Overexposure will get you dense negatives with weak colours and loss of detail in highlights.
Pushing and pulling c-41 films isn't recommended. Some laboratories will push- or pull-develop films for you but most will charge extra. So it's probably best to use the appropriate film for the appropriate situation. Again this has been my experience. I hope the above is useful for you.
No offends taken, just tiresome to ask a question and just get a load of c*ap for replies.
Yeah of course the ISO is measured for accuracy but the manufacturer, but if we take Fuji Superia as an example, I find that a slight overexposure actually gives a better result than box speed, probably it is highly subjective, though it's absolutely no problems doing it, from a technical perspective, the negs looks just fine and the colors are a tad more clear imho.
So it's this kind of thoughts and experiences I am trying to dig out from other shooters...
I believe there's another element at work that kevs is not recognizing: to the amateur market, fast box speed sells better than slow box speed. So the film manufacturers will come up with an emulsion that may be pushing the envelope a bit to shoot at rated speed, whereas if you bump it down a notch or two, it allows the emulsion to perform better. I cite Fuji Superia 400 as an example. My results with shooting Superia 400 at box speed have been simply dreadful. Clumping of grain, splotchy color, just all in all a very bad film, in my view. I can't blame the camera, which has an electronically timed shutter and which stops down the lenses accurately. And I can't blame the developing lab for it either, since they do an excellent job on other C41 emulsions I give them to process. But if I shoot Superia at 320, it becomes a totally different animal. Grain has smoothed out, colors are richer, all in all not a bad film at all.
Now, while it's true that films like Portra are not considered to be amateur films, I think nonetheless that the mindset pervades.
I share that experience with you on the Superia 400, I don't shoot a lot of it (don't shoot a lot of color) but when I do I ended up always going with 320 instead of 400, it just looks so much better!!