Them combined it kind of out of the question, as it turns out that would need 7.4 million rather than 5.9. Still, I don't think it would have had a shot at 6 million anyway. Before the holiday season, it dropped to less than 20k for a week a few times.
Generally, a good formula for decently-but-not-too-well legged games is
Sales of next year = Sales of a mid-November week *45
(It gets lower and lower sales as the year passes, but the next holiday season makes up for that).
What this means is, essentially, that I'm be expecting somewhere around 750-1000k next year for God of War 3. It should have around 500k, perhaps a tad more, left for this year, so let's say 4 million at the end of 2010. Then most likely ~ 4.9 million by the end of 2011. After that, it's going to be quite low. Something along the lines of "just a couple of hundred thousand left in its life".
So I'm going to say around 5.2 million lifetime for it. Which means that God of War 3 God of War Collection combined should nicely outdo God of War 1 2.