The Trinity study said a conservative number was 4%. Since then a lot of people said "Well, I don't want a conservative number, I want a number that has no chance of failure", so went to 3.5% or 3%. Practically I don't think that's a wise choice, a vast majority of the time most of the time, any failures comes from sequence of returns risk and the remaining percent coming from simulated bad returns coupled with a very long life.

This means that as long as you're willing to cut back on expenses if the market dips soon after you retire, 4% is fine, and it's probably not worth the extra X years of your life to try to get that number lower.