You will run higher wattage at a lower impedance but the SQ will be affected. I have read that higher resistance will produce greater SQ. This why many home stereos for surround sound are at 8 ohms. For door speakers, you would probably want to shoot for 4 ohm's. Usually one would want to go 2 ohms for a subwoofer set up to take advantage of the increased in power delivery if the amp is stable at those levels. SQ from 2 and 4 ohms may not be dramatic, but it is something to definitely think about.