It's hard to see how anyone could comfortably FIRE now on less than £500k unless there was also a DB pension in the mix or they were near State Pension age. Even though my expenses are low, I wouldn't want to FIRE in my 40's with less than £500k and no other sources of income. I've eased into a higher category since I first posted in this thread and this is purely due to inflation of the money, not lifestyle kind.
After years of low inflation the last couple of years will have been a shock to anyone that hasn't experienced it before. It's weird thinking there are a bunch of young people who have only ever been used to low interest rates and low inflation.
It's interesting you reduce the withdrawal rate as you move from lean to fat FIRE vand. I only have one number, but I would want the lower withdrawal rate on a lean number, and the higher withdrawal rate on the fat number, so I had more leeway when market times were tougher. No right or wrong here, it's just interesting how different people see things.