That's why many of us call it longevity insurance. I'm not too concerned about making my money last to age 70 or 80, or being able to spend a bit more to that point. I'm much more concerned with living long beyond 80 and being able to keep myself comfortable.
This is the point I'm going to try to model more closely when I get closer to 62. 6.5% won't come risk free but might not be an unreasonable return to use. I think I modeled 5% a year or so ago and was surprised at how late the crossover came, around 90 if I did my numbers right.
I believe one should use inflation-adjusted or real investment returns when determining the crossover age. With my asset allocation, I typically use a real return of 3.5% as a likely scenario. However, I consider the impact of lower and higher returns too (as well as taxes). A 3.5% real return puts my crossover age in the lower 80's.
I agree about the longevity insurance. For the most part, that's how I look at social security. It's extremely unlikely that I'll need the money in my 60's (I'm currently 54), but who knows what will happen over the next 30+ years. I'll re-evaluate as I approach 62, but currently I'm planning to wait until 70 before taking social security.