at this point in time, what would be the IQ of our most intelligent AI systems?
Zero.
There are many different kinds of IQ tests including written, visual, and verbal assessments, but the majority of questions are based on abstract-reasoning problems that involve creative thinking and true intelligence.
In other words, the computer would have to exhibit something that does not yet exist… "strong AI".
The intelligent computers of science fiction do not exist. At all. We are not even close. We have absolutely NO IDEA how to bridge the gap between what we can do now and what is depicted in pop-culture films. Even with cars that drive themselves and computers that play 'Go' — an underachieving mosquito possesses more cognitive intelligence than all the world's super computers …combined!
…or possibly "disqualified" for cheating.
Even if we could pre-format the questions in a style and delivery system it understands, what does memorization, attention, or speed mean in the context of a computer? I'm not even sure if a standardized IQ test makes sense in this context. It might be like asking how a computer would do in a spelling bee.
In human terms, we're not allowed to bring along reference materials to look up an answer; but how do you rectify that when reference-lookup is innate to a computer's existence? How do you measure memory when storage is non-volatile? This gets into an existential question about the nature of learning and knowledge vs. just taking a lot of notes.
Still, how do you even teach a computer what is meant by "which animal is least like the other four?" Did the computer really figure out what was being asked out of general intelligence, or is the computer simply designed to parse out IQ-style questions specifically? If you designed something with a foreknowledge of what would likely be asked, the computers of today might simply be able to "recognize" it as question-style 496.527b and plug in the variables.
But that's not general intelligence by any definition we use or understand. It's just a specialized, slick interpreter designed to parse out a specific type of standardized question. Ask it a style of question which it is not expecting, and you'll see the computer is exhibiting no innate intelligence at all.
Until we create strong AI, a computer has effectively no IQ.