Keep in mind it's probably an entirely new APU on a smaller process that does make it more efficient. The boost could simply come from the move to a new APU and not be very significant, hence why Microsoft didn't bring it up during the unveiling.
I would be extremely surprised if they took the Jaguar CPU and the existing GPU and ESRAM and paid for them all to be shrunk down to 14nm - remember teh 14 nm is a different process altogether, so each CPU and GPU would be new anyway, and ESRAM I read is not available in 14 nm.
That would be insane, its basically a full redesign of the console silicon with a new CPU, new GPU and Gddr5....basically just make a Neo design that was leaked instead it would cost the same.
If you shrink to 14 nm and redesign for FINFET process, may as well make a 4 TF GPU, it comes for free ! So if it was 14 nm, they would of easily doubled the GPU to > 3 TF and be sure MS would of said something as a 14 nm console would be at least 2 x Ps4 power.
I can only think of 2 things :
1. Maybe it is resources freed from no kinect
2. They have used a fancy new cooler and clocked a little bit higher.
Someone posted a link a few days ago of a new metallic fan which keeps GPU's much cooler - could MS be using it. Edit found it, new super cooler for Xb1 S was mentioned with coolermaster...so MS probably bumped the clock by a percent or 2.
http://techtheday.com/keeping-it-cool-coolchip-technologies-has-a-redesigned-computer-fan/