I think it's fair to use 20% digital until we have more data. I don't care about what you bought or your friends. 20% is the middle ground for a game like Halo.
So using VGC data (until 12th Dec) Phy + Dig = 3.26M and set to be 3.5M by years end. That's half of the OP prediction and that's end of story.
Until we see proof that Halo has a better Digital percentage we should stick to 20%.