Keep in mind that you can contribute to a 2015 Roth/IRA until 4/15/2016. The same holds true for subsequent years.
I suppose that there is a very small set of circumstances that could be contrived where it makes some sort of sense to do as you ask. However, a lot of special conditions would need to be meet, and even if they were meet would an extra 11K in retirement really move the needle that much?
So I would say no. One thing you do not seem to be tracking is that money borrowed from a 401K is not in the market, so there is some opportunity cost. Not as much in this case as presumably you are reinvesting the full amount borrowed.
You said you were aware of the 401K loan downsides, but it does not seem the degree of risk is registering with you.