The important changes I see on this 105 are: Vastly better front shifting and better hood shape. It should also be cheaper.
The FD alone won't help you with the 5700 front shifter. I investigated this with my 5700 and 6800 groups because I had the same idea you have.
The 11 speed front shifter moves the FD along two steps: The push releases the FD just enough to nudge the chain to the smaller ring. This allows the FD cage to act as a chainkeeper during the shift action. Releasing the button lets the FD move inward a little more for chain clearance. The 5700 lever gives up the cable pull all in one click so what does it matter what FD you are using.
Shifting to the larger ring works the same as the 5700 except the trim button is a reverse trim.