JDA2012: Just one general comment - you seem to be focussing quite highly on the technical side of things.
Once thing you don't mention is interview skills. Nobody knows how BA assess the rounds (i.e. whether one assessment method is weighted more than others). My own impression is that the interview is probably the most important element to differentiate yourself from other applicants (after all, by the final round at BA I suspect the variation in maths and technical skills isn't going to be enormous).
See if you can make friends with someone in HR / personnel or even a small business owner who can give you some feedback on your interview skills. Someone who can give honest, impartial feedback here is invaluable.
I made the mistake last year of preparing way too hard for the PILAPT and maths elements, to the point of neglecting the interview skills. No prizes for guessing which round I felt I'd underperformed in last time.