what do you mean by 'precision' ???
if you use standard regulators like 78xx , you probably need 2 volts to drop at the IC
so you have to supply 7v i/p .
But there is a another regulator that works with around 0.5 v drop out voltage , and if you draw less current the drop voltage may be even lesser [minimum 100mv]
just google out "LM2940" and check out its datasheet .