There is a correlation between MBTI type and IQ, but only in so much as certain MBTI types are better equipped for what IQ tests are designed to measure than others.
N types do much better with pattern recognition, with Ni having an advantage.
F types do much better with philosophical and abstract reasoning, with Fe having an advantage.
T types do much better with analytical and logical reasoning, with Te having an advantage.
S types do much better with detail recognition, with Si having an advantage.
However - and this is the most important part of the correlation between MBTI and IQ - an individual's performance on an IQ test is generally in proportion to their capacity with their respective functions. For example, and INFJ who has a strong Ni, moderate Fe, weak Ti, and feeble Se is likely going to score strong on pattern recognition, moderate on philosophical reasoning, weak on analytical reasoning, and feeble on detail recognition. Meanwhile, an INFJ with a strong Ni, Fe, and Ti, as well as a moderate Se is likely going to score very well across the board on an IQ test because the other functions will tend to compensate for the lesser Se.
Because of the way the IQ test is designed with pattern recognition as its primary means of interpretation, INTJs are most likely score the highest. The remaining N types generally do very well, as do the STJs. Also, because of the way the 'Gifted' test criteria is designed, the N types are much more prone to being 'Gifted'. As INFJs, we're better suited than most types to score highly on the applications measured by the IQ and Gifted tests, therefore we're going to have higher IQs. I don't think this makes us more intelligent than other types. It just validates our particular type of intelligence because that tends to be the particular type that the test measures.
Finally, for the purpose of answering the thread theme... I had an official IQ test in January of 2008 and scored a 155 (which is a misnomer, since anything over 140 is conjecture). The official IQ test is much different than most of the IQ tests floating around on the internet. Please don't assume any of them to be accurate, as they usually lack the most crucial component - they are not timed. IQ is not just a measure of reasoning capacity, but also the amount of time required to reason.