Uggh....this is the situation I've been to (with copper rather than iron), and it is hard to give an advice. What is high for one species may be totally acceptable to another. For example, a cory can survive 100x amount of copper that is lethal to some small loaches; with another metal the sensitivity pattern will be different.

Here is how I'd approach this:

Compare the amount of iron to LC50 for some fish species (there are some known numbers), if it of the same order of magnitude, it probably means that you are for real problems long term.
If the amount of iron in your water is considerably lower than LC50 for another species (say, 10 times or more), ignore the problem for now, but if you discover that you cannot keep some kinds of fish long-term, reexamine the problem, iron (if it is indeed high) should be one of the suspects. Additionally, if you start discovering rust deposits inside the tank (this happens with water rich in iron), you probably in danger.

Here is sample article that gives you numbers for the species they researched:
http://www.ansijournals.com/pjbs/2006/1807-1811.pdf
Articles of this type should not be seen as gospel, they study fish different from yours, and usually care only about short-term effects.
Still notice that of the five metals they considered, iron was the least dangerous; so the chances are that you don't have a problem.