The real question you need to ask yourself is: what do you really want out of life? You say you want to get a Ph.D. and do a startup. But why do you want to do these things? Is it because you really want to do these things, or is it because you see this as a path to financial independence? If it's the former, then by all means, go to MIT. But if it's the latter, if what you really want is the freedom that (you think) money can buy, then you should think twice. For myself, my personal goal was to live a life where I was not beholden to anyone, and I accomplished that by going to a less rigorous school, staying out of debt, and having more than my share of good luck. So that worked for me. YMMV.
One thing I've learned: the hardest part of getting what you want is figuring out what it is. Figure that our first. Don't spend four or six or ten of your best years chasing someone else's dream.