Hopefully you will get to read this thread, but I am a cardiologist, but have had the car bug ever since I was 5. A ferrari is something special, and I agree with what others have said. Depending how much debt you come out of residency with, and your plot in life will determine how fast you can/will buy your dream. One word of caution is that once you own your dream you don't have far to go to set your sights on something else, unless you are quite well off. Most guys on these forums are crazy car nuts, who happen to be more or less successful at this game of life. I have 4 small children under 10, and I have a modest ferrari (360) and I could probably have a 458, but the smile factor is present in all ferraris. I personally would ask yourself why is it that you want a ferrari 458.....image, love for the prancing horse or some other quirk. It really doesn't matter what it is, but I think buying a car that you can afford at that moment in life, is the most sage advice that has been given to me and consequently to you. I am not sure where medicine is going, but it still pays well, but not at well as it once had. Not to change your mind, but if your heart is set on a 458 then you will own one, but I agree that i might consider getting a "lesser" ferrari, as you can appreciate it sooner in life, but I would think that by the ripe age of 30 you should have enough money to get something that will make you glad you can drive. I would not mortgage my future or anything to get one, as it is just a car, albeit a wonderful experience.
Sorry to ramble but I hope that this helps.