With all the respect, choosing between RED, Alexa, Sony IS a personal matter. I would not go for Sony either because I personally don't like the images coming from the camera.
16 bit holds more information than 10 bit and most grading suites are optimized for eating r3d files. XAVC is a stranger for many, but it will probably not be an issue at all.
Working with post house where nobody can speak the DOPs language sounds like a joke, but I guess you have your reason - or no choice.