Duffles, I've verified your math.  I get 46.46%, but you're using actual payouts and I'm using theoretical numbers.  In any case, we're only about a half percent off, and your real numbers are better than theoretical ones.

Whether you break even or not all depends on how rapidly the difficulty increases.  The spreadsheet that I use to keep track of profits shows that you will probably break even and get an additional 2-3% profit.  I purchased a mining contract on July 27th with the same terms, but I may only get 94% back (I lose 6%).  This assumes that we'll repeat roughly the same difficulty increases experienced so far this year.

The difficulty is almost 24 billion now, and I'm guesstimating that we'll be at about 120 billion on January 1st.  I hope difficulty won't be that high.  It all depends on the amount of new, efficient mining equipment put into production over the next 4 months.  We were at 3.8 billion at the beginning of March, and then 18.7 billion exactly 5 months later.