And to your point about anecdotes supporting either narrative: Microsoft was defeated by open-office search company (Google vs Bing), defeated by open-office smartphone company (Apple iPhone vs Windows Phone), defeated by open-office cloud services company (Amazon AWS vs MS Azure). Perhaps we shouldn't be surprised that Microsoft has transitioned away from private offices towards open plans in their newer buildings.[1]
I've been looking for compelling evidence that proves the superiority of private offices but haven't found any. The business case studies showing superior performance that's directly caused by private offices don't exist. Yeah, surveys of employees exist but not superior business results.
[1]http://www.geekwire.com/2014/microsoft-developer-division/