Over all it will be minimal, (the heat shild will help). But it is part of a system. You want to reduse the restriction in the whole system. The engine is a air pump, basicly. If you decrease the restrictions, on the intake it will run better, if you also reduce the restrictions on the exhaust side it will run even better. Cold air gives more power (condensed) then warmer air. (I believe it is every 8 deg colder, gives 1 hp more power). (other factors contrubute also,like BMPressure and humity).
If you think of it as a water pump (engine) and you increase the hose size going into, and out of the pump the pump will pump more water.