Also what is high-impact? Nature Reviews, Neuron, Science, NEJM, Lancet (IF: 5+?)
Hahaha... ok, two ways to answer this:
An IF of 5+ is certainly one way to assign the "meaningfulness" of a publication, and especially if you are a PhD trying to build your resume, you probably want to get in here with a 1st author pub.
Anything that is in Nature/Science/Cell/NEJM/Lancet are considered top class, and these publications are a mixture of "big science" (big $$$$) and very clever ideas that work and change not only one specific field, but are applicable to other fields as well (hence why nature/science are multi-disciplinary)
HOWEVER, it really depends on your field. Cancer journal's IF's tend to be higher than other fields, just because there is so much movement in that field. However, having a significant discovery in the field of, say, endocrinology could go in either:
a) One of the major multi-disiplinary journals (Nature/Science), but it would have to be REALLY big (i.e. there is no shame in not ending up here!)
b) In the top endocrinology journal (assuming it isn't clinical in nature, in which NEJM/Lancet would be the target) - just for example, (the number is made up) the top endo journal might have an impact factor of 3 since there is less need to cite these articles since the field may move considerably slower, BUT you have still made a major contribution to your field, and you would be invited to talk at endo conferences, etc.
In conclusion, correct me if I am wrong, but the IF of journals in fields that are "hot topics" and/or can be supported by in vitro work tend to have higher IF because knowledge (and publications) are always coming out of these fields. However, in the fields where more in vivo work is required, it also requires more $$$/time, and publications appear less frequently. This gives those journals a lower IF.