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From what I gather the narrower the filters the more precise your tricolor imaging will be. a Ha 3nm will give you a better result than a 7 or 13nm when you recombine your channels with the adjacent Sii for example, no channel bleed. So the narrower the better, but the dearer as well.
The other thing to consider is reflections. Some have better coating than others.
Finally I don't know about fast versus slow scopes but I know that the light angle of incidence on the filter does matter. Filters are designed to have light hitting the glass square. If the angle is too big then they don't work the same way. This can be a problem with an hyperstar for example where the light cone is very steep and I hear that in those circumstances a wide bandpass filter (Ha 13nm for example) would be recommended vs. a 3nm.
That's as far as I know about it. Sure others will drop in with better explanations.
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