If you talking image dynamic 6x9's then the 6x9s are better than the 6.5's. The only reason 6x9's have lower sq is because few companies make higher end version of the speakers in that size. Beyond that though the 6x9 has more surface area so a higher effeciency and lower extension. In the case of the ID drivers, it's the same speaker with a bigger cone, think of it as stepping up to a funny shaped 8, cuz that's basically what it is. Anway I ru xs69's in my kick and they sound very good.