Quick answer: in 45,000 simulations of a 35-year, $1M retirement, each extra 1% of spending costs progressively more — 3%→4% costs 1.8 points of success, 4%→5% costs 7.3, 5%→6% costs 16.1, and 6%→7% costs 18.3 points, down to a 56.4% coin flip. The same $10,000/year raise can be ten times more dangerous depending on where you start.