I agree with Bamm1. The k900 is not about being an all-in-one grand tourer, it's purely a luxury car intended to go up against the E-Class, A7, 5-series, etc. The Stinger is more comparable to the A4, Giulia, and C-Class.
Also in my opinion, the Stinger outclasses the k900 in looks by leagues, and that's definitely an important part of a car for me.