btw,even if you were going to go w/ 4 15's, its a "rule of thumb" that you need at least 2.5-3 cubes per 15 and thats not counting the displacement of the speaker.i don't think you have 10-12 cubes in a G35. i guess it depends on if you can find a 15 that only uses 1.5-2 cubes per speaker(plus...