It will pass Halo 3 eventually regardless, though how many units it will sell depends on MS "milking" of the franchise and the new xbox. MS said they wanted a new Halo less then every three years, so how many units will this sell if a new Halo comes out in two? A new Xbox would also completely kill off sales. I think it will pass Halo 3 but I'm not sure how much it can do against Modern Warfare 2, considering people will still be buying that even with Black Ops out.

It was overtracked afterall

by 5% which is nothing, so we're still correct

Well, I said it was overtracked by 5-10% (worldwide). It isn't much, but it means that Reach didn't outsell Halo 3: probably it sold less.

using VGC numbers Reach outsold Halo 3, using NPD numbers Halo 3 outsold Reach.

In the end it could be either way, since both options are equally likely.