Nubbe Centre

[Kaden]

You do lose a bit of tower-takedown-ability with AA over MM; 40% of 150 is 60 additional turret damage, versus the full 70 of the manamune's bonus damage. But that's not enough to be noticeable, and certainly doesn't outweigh the AP of Archangel's.

So you know, your damage to towers only factors in AP if 40% of your AP is higher than your AD. You'll get 0 bonus tower damage with an AA versus the 90 (given your numbers) you'd get from Manamune.

EDIT: I don't build Manamune because the mathcraft came out in its favor. I build it because I've played a lot of Ryze and found it to be a more useful end-game item.