Mileage for used sti 2017+

All of this is so incredibly subjective on how the car was maintained. I've seen STI's with 100k miles that I would buy over some with 20k.

^^This. Look at the owner & maintenance history. Avoid cars with cheap aftermarket parts and/or owners who talk like they just stepped out of filming fast X.

Find something stock with no mods, make sure they weren't removed just before the sale. Buy the nicest one you can possibly find, it will be cheaper in the end.