I'll apologize for not checking my sources before responding...but my recollection is that it was possible to estimate IQ from SAT scores back before the reentering decades ago (I think in the late 80s?), but since then, changes in the population that takes the SAT (more diverse, which is good, but less homogenous, which makes it less comparable to past research, and less selective, which lowers the meaningful ceiling), and thus the norms, and changes in the nature of the test, away from more reasoning, and toward more achievement, have flattened its usefulness for estimating IQ. IOW, it no longer spreads the cognitive upper end of the population as well as it did a generation ago.
It is still possible to make some estimates based on 7th grade SAT scores, but it is just that, a rough estimate.
The PSAT is a different question. The most recent PSAT and SAT are on the same scale, which makes them a little easier to convert, but the old PSAT was not quite as comparable. Did you take the new PSAT, or the old one? You can also just use your direct percentile, if you took it at typical age (I assume you took it this past school year). That's a much simpler way of estimating ability from achievement, although it's still just that--an estimate.
I looked at that quora answer: that is certainly a plausible approach to estimating IQ. I do know, though, anecdotally, that it doesn't necessarily provide much precision, since my personal data set of multiple related persons has simple differences of 10-50 points between SAT-generated estimates and individually-administered assessments, in both directions. And again, much of the data Lubinski, et al used was from prior versions of the SAT. I would say, though, that if a person is at or above the 50th %ile in the data set, that is a pretty good indication that that person has high cognitive gifts, since the pre-qualifying criteria for participating usually include previous assessment data in the 95th %ile or above (about 125 on tests like the CogAT).
