Originally Posted by Davidka

carbon shoes last a loooong time, probably longer than any metal based shoe.

Like other's said, don't sweat the oil percentage. The reason 30% always has lower oil % is because nitro is an oxygenator and allows you to pass more fuel through the engine (hence more power) if you have 20% fuel with 12% oil and 30% with the same 12% oil, with a correct tune, you're actually passing more oil through with the 30% fuel.