Well, James (DNA) Watson had a purported IQ of 125. William (transistor) Shockley's was in the low 130s. Both these men are generally considered geniuses. Shockley considered himself a second or third level (as he put it) genius. I think the average PhD has a 140 IQ. Durk Pearson's IQ wasn't measurable, but I hesitate to think of him as a genius. That might be because he's so up there and I'm not.
I put "genius" in scare-quotes because IQ testers will say that anyone with a high enough IQ (150 or 160 are typical lower limits) is a genius.
But genius, as most people understand it, is obviously not reducible to IQ. To put it in plain language, you can be extremely smart without being particularly creative. Ramanujan, Einstein, Feynman, et al. were extremely creative, not just extremely smart.
Also (and this pushes us outside the limits of conventional intelligence testing), most genius-level capabilities are specialized. Ramanujan, for instance, was highly creative in certain areas of mathematics; I gather from my (very limited) knowledge of his life that he wasn't highly creative at anything else. Mozart was highly creative in music; nothing special otherwise.
Standard IQ testing procedures assume a normal distribution (a bell curve) of scores in the human population, with a population mean of 100 and a standard deviation of 15. Two standard deviations above the mean yields an IQ of 130. That's higher than the IQ's of roughly 98% of the population, but "genius" level IQ (see disclaimer above) is more than three standard deviations above the mean.
You've confirmed what I meant to imply about Ayn Rand being a slow reader. Her slow reading was a consequence of other unusual cognitive abilities. But of course it came at a cost--like not being willing to put the time in to read John Rawls' book.
I'm not claiming comparable scale here, but I read articles in academic psychology very slowly, compared to nearly anything else I read. It's because I'm constantly trying to figure out what's being assumed, or what the unstated implications might be. I can read a novel in French (a language that I didn't learn till my teenage years, and that I have to use different brain centers to process) faster than most psych journal publications in English.
An IQ test score is considered an objective measurement of (some types) of intelligence because it's a number that can be compared with other numbers. I understand IQ tests were developed and/or first extensively used as a quick way of determining who was officer material and who wasn't in WWI.
I think that someone who isn't a genius can create something of genius. I think genius can even be a flash in the pan. But when you get to the top of the heap it's just staggering, especially with the math and science guys closely followed by the classical music creators. Wow! As for Ayn Rand, I think she was absolutely a genius who peaked in the 1940s with "The Fountainhead" and the first years of writing "Atlas Shrugged." But I then think she effectively got stuck inside her own creations. As Nathaniel Branden said (regarding "Atlas"): "and wasn't coming out." (Not necessarily an exact quote.) You aren't a genius if you've created nothing to show for it. I think that that is the common thread in considered genius.