There is a fair amount of imperical data that suggest at least wild caught sa fishes can suffer under hardwater both short and long term. However as previously stated the number of studies are not many.
@Uberhoust link to an older thread does have a link to an peer reviewed paper that study of dead fishes indicate that hardwater was having a negative impact on tetra via calcium buildup in their system.
The problem with threads like this (nitrate is another common thread; as well as organic buildup due to lack of or insufficient water changes) is that it is hard to 'prove' these things because you need very large control experiments with impeccable technique and this is something that a home user isn't going to be able to execute. I.e, it has to be done in a lab with sufficient $$.
However as a home owner there has been emperical evidence that all these things matter - more so for more sensitive species.
Of course the next question might be how much does hard water at level x shorten species y life span - is it hours, days, years.... can you imagine the sort of study required to answer that question. It could potentially take 100 years for a species like clown loaches; though once underway the answer could become obvious.
I can't authoritively answer any of these question though i know it doesn't take much organic buildup to see negative impact (disease in the form of bacteria infection) on some of my more sensitive fishes. I remember some guy telling me 78 was fine for wild caught discus yet the ones i ahve throw a tantrum if the water drops below 82 (83/84 seems to keep them happy).
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Since most of my fishes are wc cichild (mostly dwarf but i have a few geo and festivum); i try to keep my tds below 50 (below 13 for blackwater species) and nitrate well below 5.
This doesn't answer your question per sey but you wont be able to get a precise answer - i.e, if your water is 200ppm hardness it will live x less; you will find plenty of people who say 200ppm is fine but they can't say if it shorten the life by 1 day or 1 year or 50% or 80% and i don't think you will ever find an answer of that nature. I will say that lower is better and conversely lots of catappa leaves (or similar) is also better as the tannis actually provides more than tint.
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So did i say anything useful - not really but i'm not sure i could.