Using OPT for takeoff performance , and doing often derate/assumed temp, I can say it will give you different stab trim in case of derate.
By doing derate you may sometime gain a few% reduction on takeoff, weight/rwy permitting. So you'll have a different N1 setting for 22k or 20k derated, hence a different stab setting.
If you'll get the same N1 (derate and assumed combined) ,then a derate is not helpfull.