Here lies my knowledge. Some of it has already been mentioned but use it how you wish.
Full length intakes add more hp on lower speeds than higher (right up to the VTEC operation point). Short air intake system added more hp on higher speeds (right on the VTEC operation point) on a Dyno Test (with the hood open) but lost power in the real world due to heat. A downside of short intakes is that it places the open-element filter in the engine compartment where it is forced to ingest a diet of hot air. General rule of thumb, power output is reduced by 1% for every 10 degree increase in air temperature. Colder air has more oxygen molecules.