I'm sure there are a lot of charities that struggle to donate 10% of what they raise (e.g., some 5 year old sells lemonade for 50 cents a cup then donates the proceeds to his youth group). I would think when you start to exceed about $5k in annual donations the marginal cost of operations begins to dramatically decline. At $2 billion, you ought to be donating 95%+ to charity or have your 501c3 card pulled, because you're just stealing from people under the pretense of charity.
5% of $2 billion is $100 million fwiw. Most mutual funds manage that amount of money at around 1%, including marketing a fund raising costs, and paying people a helluva lost smarter and more worthwhile than the Clinton subhumans