People don't want the doctor with the highest IQ. They want the one who KNOWS the most.
This isn't like mathematics, where IQ is what separates the average college professor from the Fields medalist.
With the exception of MD/PhDs, physicians aren't inventing anything. We are simply applying known solutions to a finite, albeit huge, set of problems.
Indeed, beyond a certain threshold of intelligence, which 99.9% of doctors possess simply by virtue of having made it into and through med school, the real bottleneck to success in medicine is simply how many facts you have crammed into your head. This, as others have pointed out, is largely a function of how much time you have put in. An IQ of 200 is worthless if you never opened up a medical text...unlike in math, where autodidacts like Ramanujan are able to dominate with only a God-given intuition for the subject in the setting of minimal formal education.
The theoretical ideal then, in terms of raw aptitude for medicine, would be the person with savant-like memory a la Rainman (which is DISTINCT from IQ) who also possesses an insane work ethic, enabling him to eat, sleep, and breathe medicine all day everyday until he developed an encyclopedic knowledge of it.