Curious to know which Spending Model in Firecalc you used that gave you the most confidence in the resulting % success rate. I'm guessing y'all used them all but is there one you wanted to see a 95+ % success rate to give you the most confidence in your plans?
Personally, I rely most on the Manual Spending option.
As your post clearly says, there are two questions here.
1. What model do you use to test your RE plans in FireCalc?
2. What have you been doing since you actually FIRE'd?
I've been fully FIRE'd (no PT job, no working DW, no hobby business, no bluebird inheritance, etc.) for going on 13 years. (Not that there's anything wrong with any of those scenarios! They're just not what I'm doing.)
1. For original planning, I used a conservative forecast of my anticipated retirement budget + the constant spending model. There was enough in my forecasted budget to accrue for lump sum expenditures such as new cars, remodels, etc. I chose historical CPI.
2. For the first 12 complete years of FIRE, we've easily spent less than the original budget + inflation and were probably too conservative in our planning. I chose not to remove the dollars not spent from my FIRE portfolio and it's been a great time for portfolio growth, so things are looking fairly rosey in terms of current portfolio value.
Each year, our actual withdrawal amounts are calculated manually with our FireCalc budget as a guideline. That is, we use "constant spending" to test our future plans vs historical data in FireCalc, but that outcome is only one of several factors that influence what we actually do when the time comes in terms of spending.
We've learned that, by far, time is our most important and scarce resource. We make general plans within the broad financial guidelines of "FireCalc constant spending" and then modify them as we go along to maximize our enjoyment of our time generally within our broad spending constraints.
DW RE'd at 55 and I at 58. (Actually, I'm not retired, I'm "long term unemployed as I was unceremoniously canned by MegaCorp as I neared career end.) We're both 71 now. So far, we have definitely not seen any reduction in spending as we've aged. We do pretty much everything we'd like to do but there continues to be a list of activities we would gladly trigger if our budget were bigger.
In general, budgeting time is a LOT tougher than budgeting money. It seems so scarce and hard to control. Budgeting finances to support using time pleasantly is the target so we don't assume less spending power going forward.