My wife and I are ~40, and have 3 kids. When the mortgage is gone and kids are on their own, we estimate our expenses to be ~$45k/year, plus taxes (should be minimal) and health insurance (who knows?).
We enjoy our jobs, and had planned on sticking around in at least a part-time capacity, probably until ~55 or so -- partially because of benefits like 50% paid college tuition for our kids. I was using FIRECalc to investigate some scenarios involving working part time, and it was eye-opening.
With current expenses, I can afford to switch to an 80% work schedule from now until the mortgage is paid off + the kids start graduating out of private school (we know this is un-Mustachian, and we're cool with it) in ~6 years, and then work 50%-60% after that until retiring fairly young. FIRECalc gave me a 96% success rate of withdrawing $75k/year from age 50-90. That's $30k more than our expected expenses, which is probably more than an adequate buffer to account for taxes and health insurance.
If we got into OMY syndrome and kept working 1/2 time all the way up to the ripe age of 55 (we'd be able to maximize the 50% tuition benefit this way, coincidentally), FIRECalc says we could withdraw $97k/year at a 96% success rate.
What struck we is that we may have saved too much already for our circumstances. We're neither exactly trying to FIRE (unless you consider age 50-55 in your definition of RE) nor maximize wealth per se. Our goal is to live a life that we are satisfied with, which includes working a bit less and spending a bit more time building awesome memories with each other and the kids.
It seems pretty dumb to just keep plugging away at full-time work when I don't need to. I'd appreciate any opinions and perspectives, especially from those who are considering a similar career-unwinding, or who have actually done it.