The 11-39t sprocket installs nicely
Of course, even taking into account that it's 0.2 steps slow at one particular spot, the compatibility works well. I also installed a 105 rear derailleur, and since it maxes out at 36t, it's even roomier and works great.
However, since I'm using a single chainring, this works, but for those running 2 chainrings, it seems you'd need to use a 105 derailleur and reduce the chainring spacing to make it work...
