Believe me, I've been obsessively reading threads on VPW for the last year or so. Interest Compound (I think that is his/her name) said something that really altered my worldview recently: that the withdrawals should simply be seen as income, and therefore orthogonal to expenses. (Several of you have said the same thing, above, but maybe it was just something about the way he/she said it...) Looked at that way, it really is no different than my own income, which has varied pretty wildly over the years I've been in (and out, for schooling) of the workforce.
I don't have to make a decision yet, because even under an optimistic scenario of 5% withdrawals from the beginning, I don't retire for another 2 years. That is, unless I predict lower expenses--which especially if I'm going to do VPW, I am loathe to do, since I would need the ability to be flexible with my expenses when "income" is low. Right now, about 50% of my predicted retirement expenses are "necessities," and 50% are essentially luxuries.
Yes, I am almost certainly working longer than I need to. But as we've all discussed ad infinitum, it's really, really hard for many of us to walk away, especially from a good, very stable income.