It's probably not a bad place to start.
It partly depends on how those categories will be invested: equities, bonds, or some mix. Then I would see how that mix has performed long term, or over a period similar to what you think the future x years will be like (polish up yer crystal ball!
) to get an idea of a range
of values to try.
FWIW, I did run ORP with 5% in all those categories, and then ran it @ other values down to 1% real return (I haven't run ORP in a while, so I forget off the top of my head how it's set up to work).
I tend to run those things on the conservative to ultra-conservative side. I'm not so concerned with the great years; I'm more concerned about getting through periods of lean