There was an episode of Planet Money just a couple of months ago that says Buffett is indeed on track to win the bet:
http://www.npr.org/2016/03/10/469897691/armed-with-an-index-...
CAGR of the S&P500 from 1/1/2008 until the end of 2015 was 6.5%. No idea what fund of funds they used but it's probably not going to be trivial to beat that (+whatever 2016 holds) over the time span after fees.
[0] http://longbets.org/362/