ok..my room is 21'by14' in my basement and I have decided on the Optoma HD70 front projector or the Mitsubishi that is in that same price range. I am wondering what size screen would be the best....I want to have 2 rows of 3 seats at one end of room, so the closest person should be about 15 feet or so away, I want the biggest screen possible...........also just one more thing, my dvd player currently consist of an Xbox..not the 360 but the original one, do I need to upgrade that for better picture ??