My only disagreement is with your last statement that once you "go above 700 in a subject area, scoring higher really makes no difference." All other things being equal, I think that a 2400 (800 x 3) or even a 2250 (700 x 3) might garner an applicant a better chance than an applicant with a 2100 (700 x 3) of gaining admission to an elite college.
Yes, as MIT admissions statistics confirm
http://mitadmissions.org/apply/process/stats . The increase in the admissions rate going from the 700-740 range to the 750-800 range is larger than the increase going from 650-690 to 700-740.
You need to be careful here about mistaking correlation with causation. While statistically, it might be true that admission rates correlate to the highest scores, my experience leads me to believe that is not the *reason* for the admissions.
The elite schools (including the one I attended) have the ability to fill their entire class with valedictorians, or those with 2400 on their SAT. Yet they do not. I had a few classmates with scores averaging around 600 per subject! The fact of the matter is that SAT scores are not a huge factor in the decision-making process (yes, this is coming from someone who makes a living tutoring the SAT.) The top-tier schools are looking to create a class of very special individuals and thus are looking much more closely at what unique contribution each applicant can make to their student body. People who can distinguish themselves from the masses of other high-acheivers are the ones who get in.
In less competitive schools those perfect SAT scores can make a difference, but because a 2400 actually might serve to distinguish someone at that school, unlike at a Harvard, Stanford, MIT....
Again, my experience is strictly anecdotal (and a little bit based on conversations with admissions departments), but it is extensive. Once a kid is over 700, that SAT score isn't going to keep them *out* of anywhere. By the same token an 800 will never get a kid *in* at an elite school. Once you are in the 700-800 range, the other parts of your package are going to have a much more substantial impact on your application. While it may be true that there are more interesting applicants who score an 800 than interesting ones who score a 700, the interesting applicant who had the flu on test day and scored a 700 as a result has no less chance of getting in than he would have had with an 800.
