I thought more of something like this:
Start with 4%
If the earnings for that year are 10% then put 6% in another fund and use the 4%
If the earnings are less than 4% then take money from the reserve fund to equal 4%
Hopefully your reserve will build enough to use it as a 'splurge' account at some point while your nest egg remains safe.
I guess in the end it's just as easy to take the 4%
