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IQ and intelligence are different things.
Human Intelligence can be broadly defined as the sum of a person's fluid and crystalized intelligence, fluid intelligence is correlated with IQ ( pattern recognition, visual pattern manipulation, speech generation, processing speed ) and crystalized intelligence is essentially the overall accumulated knowledge, the hard drive. So far we've only had a handfull of people with a high fluid and crystalized intelligence, such as Von Neumann, Da Vinci, Tesla etc.
As for IQ I'd say the maximum we could possibly reach through eugenics and random probability is probably aroud. 6-7 SD or 190-205, with the addition of certain quirks ( such as a perfect memory, abstract mathematical ability ), we could theoretically surpass 200 but that would be insane, since no IQ test would be even remotely capable of measuring that high.