Two quick points:
IQ scores are not a "measurement" of anything.
Two mental ability tests that correlate very highly in the order by which they sort test-takers will still, at best, only predict a RANGE of scores on one test for any given score on the other test.
Some Harvard students surely post high IQ scores, and some post merely above-average IQ scores. We haven't specified which brand name of IQ test we are talking about here, nor has anyone referred to any actual empirical data about IQ tests (so named) themselves, rather than referring to other mental ability tests.
For much more, see http://learninfreedom.org/iqbooks.html
Bottom line: the average IQ at Harvard is irrelevant to any concern of any serious applicant.