for a 5x5 room for 4-5 - 5 gallon bucket plants, how big should the aircooled reflector be? the wing on the top? 8" ?
Use the biggest reflector you can find with a 1000w MH/HPS... as for the air cooled part, 6" or 8" should be fine. A 6" inline is all you should need for that size room.