Alright, it looks like we a have a good clue to how much Microsoft has overshipped the Assassin's Creed bundle. Here's Abdiel's assessement:
"Our DCs have had a just absolute ton of those AC bundles since December, and we're finally bleeding them down to the last vestiges. And really, even that's become a crawl, because the Halo bundle has largely just replaced sales of the AC bundle, so there's no increase in speed of sales, at all."