In a Wall Street Journal posting titled the 'Third Rail' of Nonprofits, a Bridgespan rep was interviewed to discuss some thinking about the ever-so-onerous topic of overhead.
Without reading more than the interview, I beleive that Bridgespan missed the point. In reality, there really isn't such a thing as overhead -- just, the cost of delivering service. And the measure: total cost to total results. If you don't like the results, don't give. Results may reflect bad budgeting/spending on the part of the nonprofit but like any business, those decisions are up to the owners/board. Bad decisions, poor results. And, no, there is no perfect standard. Some services cost more to deliver than others. The successful board figures out what the reasonable costs are to achieve great results.