
Assuming I calculated correctly, there appears to be an inflection point around 25% or so. For example, there is more gained in increasing your savings rate from 10% to 15% than there is from increasing from 50% to 55% (not to say don't do this, just to say that the reduction in years to FI isn't as large).
As you'd expect, it supports the usual rules of thumb:
1. Jacob says you can retire in a few years saving nearly all of your paycheck
2. Save 15% and retire at the usual age (30 years or so from when you start working)
I ran it with different interest rates and the curve looks the same but the years to FI increases or decreases depending on the direction you go.