I truly wish you the best of luck, and for an excellent outcome.
One thing - you just can't say "why I'm getting a PhD", even from an elite school, the way you'd say "why I'm getting a law, medical, or business degree". Even if you've been admitted to an elite program, you can really only say "why I'm rolling the dice on the possibility of getting a PhD".
At elite programs, there is essentially no involuntary attrition in JD, MD, or MBA degrees. Yale law school has no 1L attrition. Columbia's JD 1L attrition is 0.3%. Attrition rates at elite med school is typically well below 1%.
http://taxprof.typepad.com/taxprof_blog/2008/04/law-school-r...
(I'll stop with the googling of links here...)
Attrition rates for engineering PhD students appear to be about 33%. This (to me, atrocious number) is way better than science or humanities.
http://www.insidehighered.com/news/2007/12/07/doctoral
Unlike JD, MD, MBA programs, I don't believe that the numbers are better at elite schools.
http://www-inst.eecs.berkeley.edu/~wicse/index.php/papers/li...
I dunno, maybe Berkeley is a risky program, it is a notoriously harsh school.
In spite of all I've said, I'm always hesitant to give anyone advice. There are still remarkable careers to be had in academics. Good luck.