Originally Posted by XT43

+1. Spec C is the best but probably not worth it as they're harder to come by and a lot more $$$
Part numbers if you're keen

Aus Spec WRX rack: part # 34110FE130 (16:1)
Aus spec STi rack: part # 34110 FE510 (15:1)
JDM Spec C rack: part # 34110FE440 (13:1)

You'll have to get and STi rack of the same year or less GD as yours cos I'm pretty sure they changed the mounting positions from 05 onwards which apparently can be changed but only after a fair bit of fucking around.