Selling status is a huge part of the consulting business, especially for a company like McKinsey. I find it quite likely that women are less effective (in most modern-day business social environments) at producing the sort of status signals that McKinsey sells

I agree with this, particularly if "effective" includes "interested." But the interesting question is what McKinsey thinks about all this.

Based on my knowledge of the industry, I would guess that 60-70% of entry-level consultants and 80-90% of partners at McKinsey are male.

I would probably agree with this too. And that a lot of the women in these numbers receive special incentives like less demanding schedules. But again, the interesting question is what McKinsey thinks about this. What would they say if they were accused of discrimination?

Edit: For kicks I looked at the McKinsey web site for the city where I am located (New York). The site lists some 25 senior managers. Based on the photographs, 4 of the 25 are female. So it looks like your estimate was right on the money.

http://www.mckinsey.com/global_locations/north_america/northeast/en/our_people

Again the question: How would McKinsey respond to the observation that 84% of its senior management in New York is male?