If you are entering your data into FIRECalc correctly and it gives you 95%+ success rate at greater than 5% W/D rate, there is no reason to limit yourself to 4%. FIRECalc was designed to include all aspects of your retirement income in your withdrawal scheme, and the 4% rule applies only to your nest egg, excluding pension, SS or other income.
FIRECalc says I can start out at 5.8% for the first few years (I retired at age 58 - living off my portfolio only), but I know when SS kicks in the withdrawals from my portfolio will decrease to well below 4%. That's one of the real values of FIRCalc.
Numbers is hard
Retired in 2005 at age 58, no pension