Go with 9s if you like them. Personally, I've never bought into the part about heavier strings resulting in better tone. As mentioned above, Iommi played 8's and had monstrous tone! At the very least, whatever minuscule difference there is in tone will be more than compensated for by your better playing on strings that feel comfortable to you.
I've gone through stages of playing heavier strings to try it out and lighter strings to try it out. I still sound like me, so I decided to play what I feel the most comfortable with......and that depends on the guitar and the tuning.